[Driver] allow Android triples to alias for non Android targets

[nickdesaulniers]

Summary

Partial revert of r330873 ('[Driver] Reland "Android triples are not
aliases for other triples."')

While we don't want -target *-linux-android to alias to non
*-linux-android libs and binaries, it turns out we do want the
opposite. Ie. We would like for -target *-linux-gnu to still be
able to use *-android libs and binaries.

In fact, this is used to cross assemble and link the Linux kernel for
Android devices.

-target *-linux-gnu needs to be used for the Linux kernel when
using the android binutils prebuilts (*-linux-android).

The use of -target *-linux-android on C source files will cause
Clang to perform optimizations based on the presence of bionic (due to
r265481 ('Faster stack-protector for Android/AArch64.')) which is
invalid within the Linux kernel and will produce a non-bootable kernel
image.

Of course, you could just use the standard binutils (*-linux-gnu),
but Android does not distribute these. So this patch fixes a problem
that only occurs when cross assembling and linking a Linux kernel with
the Android provided binutils, which is what is done within Android's
build system.

[srhines]

Please remove the reference to b/X in the commit message. LLVM doesn't allow internal bug numbers, and you described the issue well enough without it.

[danalbert]

LGTM

lib/Driver/ToolChains/Gnu.cpp

/*static*/ void Generic_GCC::GCCInstallationDetector::CollectLibDirsAndTriples(
     SmallVectorImpl<StringRef> &BiarchLibDirs,
     SmallVectorImpl<StringRef> &BiarchTripleAliases) {
   // Declare a bunch of static data sets that we'll select between below. These
   // are specifically designed to always refer to string literals to avoid any
   // lifetime or initialization issues.
   static const char *const AArch64LibDirs[] = {"/lib64", "/lib"};
   static const char *const AArch64Triples[] = {
       "aarch64-none-linux-gnu", "aarch64-linux-gnu", "aarch64-redhat-linux",
-      "aarch64-suse-linux"};
+      "aarch64-suse-linux", "aarch64-linux-android"};
   static const char *const AArch64beLibDirs[] = {"/lib"};
   static const char *const AArch64beTriples[] = {"aarch64_be-none-linux-gnu",
                                                  "aarch64_be-linux-gnu"};
 
   static const char *const ARMLibDirs[] = {"/lib"};
-  static const char *const ARMTriples[] = {"arm-linux-gnueabi"};
+  static const char *const ARMTriples[] = {"arm-linux-gnueabi",
+                                           "arm-linux-androideabi"};
   static const char *const ARMHFTriples[] = {"arm-linux-gnueabihf",
                                              "armv7hl-redhat-linux-gnueabi",
                                              "armv6hl-suse-linux-gnueabi",
                                              "armv7hl-suse-linux-gnueabi"};
   static const char *const ARMebLibDirs[] = {"/lib"};
-  static const char *const ARMebTriples[] = {"armeb-linux-gnueabi"};
+  static const char *const ARMebTriples[] = {"armeb-linux-gnueabi",
+                                             "armeb-linux-androideabi"};
   static const char *const ARMebHFTriples[] = {
       "armeb-linux-gnueabihf", "armebv7hl-redhat-linux-gnueabi"};
 
   static const char *const X86_64LibDirs[] = {"/lib64", "/lib"};
   static const char *const X86_64Triples[] = {
       "x86_64-linux-gnu",       "x86_64-unknown-linux-gnu",
       "x86_64-pc-linux-gnu",    "x86_64-redhat-linux6E",
       "x86_64-redhat-linux",    "x86_64-suse-linux",
       "x86_64-manbo-linux-gnu", "x86_64-linux-gnu",
       "x86_64-slackware-linux", "x86_64-unknown-linux",
-      "x86_64-amazon-linux"};
+      "x86_64-amazon-linux",    "x86_64-linux-android"};
   static const char *const X32LibDirs[] = {"/libx32"};
   static const char *const X86LibDirs[] = {"/lib32", "/lib"};
   static const char *const X86Triples[] = {
       "i686-linux-gnu",       "i686-pc-linux-gnu",     "i486-linux-gnu",
       "i386-linux-gnu",       "i386-redhat-linux6E",   "i686-redhat-linux",
       "i586-redhat-linux",    "i386-redhat-linux",     "i586-suse-linux",
-      "i486-slackware-linux", "i686-montavista-linux", "i586-linux-gnu"};
+      "i486-slackware-linux", "i686-montavista-linux", "i586-linux-gnu",
+      "i686-linux-android"};
 
   static const char *const MIPSLibDirs[] = {"/lib"};
   static const char *const MIPSTriples[] = {
       "mips-linux-gnu", "mips-mti-linux", "mips-mti-linux-gnu",
       "mips-img-linux-gnu", "mipsisa32r6-linux-gnu"};
   static const char *const MIPSELLibDirs[] = {"/lib"};
   static const char *const MIPSELTriples[] = {
-      "mipsel-linux-gnu", "mips-img-linux-gnu", "mipsisa32r6el-linux-gnu"};
+      "mipsel-linux-gnu", "mips-img-linux-gnu", "mipsisa32r6el-linux-gnu",
+      "mipsel-linux-android"};
 
   static const char *const MIPS64LibDirs[] = {"/lib64", "/lib"};
   static const char *const MIPS64Triples[] = {
       "mips64-linux-gnu",      "mips-mti-linux-gnu",
       "mips-img-linux-gnu",    "mips64-linux-gnuabi64",
       "mipsisa64r6-linux-gnu", "mipsisa64r6-linux-gnuabi64"};
   static const char *const MIPS64ELLibDirs[] = {"/lib64", "/lib"};
   static const char *const MIPS64ELTriples[] = {
       "mips64el-linux-gnu",      "mips-mti-linux-gnu",
       "mips-img-linux-gnu",      "mips64el-linux-gnuabi64",
-      "mipsisa64r6el-linux-gnu", "mipsisa64r6el-linux-gnuabi64"};
+      "mipsisa64r6el-linux-gnu", "mipsisa64r6el-linux-gnuabi64",
+      "mips64el-linux-android"};
 
   static const char *const MIPSN32LibDirs[] = {"/lib32"};
   static const char *const MIPSN32Triples[] = {"mips64-linux-gnuabin32",
                                                "mipsisa64r6-linux-gnuabin32"};
   static const char *const MIPSN32ELLibDirs[] = {"/lib32"};
   static const char *const MIPSN32ELTriples[] = {
       "mips64el-linux-gnuabin32", "mipsisa64r6el-linux-gnuabin32"};
 

test/Driver/android-gcc-toolchain.c

+// Test that gcc-toolchain option works correctly with a aarch64-linux-gnu
+// triple.
+//
+// RUN: %clang %s -### -v --target=aarch64-linux-gnu \
+// RUN:   --gcc-toolchain=%S/Inputs/basic_android_ndk_tree/ 2>&1 \
+// RUN: | FileCheck %s
+//
+// CHECK: Found candidate GCC installation: {{.*}}/Inputs/basic_android_ndk_tree/lib/gcc/aarch64-linux-android/4.9