clang: add support for hard float musl linux targets.

[martell]

Summary

This might seems a little confusing on a first look but llvm::Triple::GNUEABIHF generally refers to a glibc hf triple.
We just apply the same logic to llvm::Triple::MuslEABIHF because if just refers to the c library.

There doesn't seem to be an existing testcase for the llvm::Triple::GNUEABIHF logic.
The only question I have is should we apply the same logic for FreeBSD targets with musl?

[krytarowski]

Next time please send patches with git diff -U999, it will be easier to review.

[martell]

@krytarowski done :)

[krytarowski]

I'm not sure about Triples here.

[martell]

@krytarowski for context this is the triple alpine expects
https://git.alpinelinux.org/cgit/aports/tree/main/clang/clang-0004-Add-musl-targets.patch?h=3.6-stable
Would be nice to get this in shape so we can use alpine in conjunction with docker files added by rL306810

lib/Driver/ToolChains/Gnu.cpp

case llvm::Triple::aarch64_be:
     LibDirs.append(begin(AArch64beLibDirs), end(AArch64beLibDirs));
     TripleAliases.append(begin(AArch64beTriples), end(AArch64beTriples));
     BiarchLibDirs.append(begin(AArch64beLibDirs), end(AArch64beLibDirs));
     BiarchTripleAliases.append(begin(AArch64beTriples), end(AArch64beTriples));
     break;
   case llvm::Triple::arm:
   case llvm::Triple::thumb:
     LibDirs.append(begin(ARMLibDirs), end(ARMLibDirs));
-    if (TargetTriple.getEnvironment() == llvm::Triple::GNUEABIHF) {
+    if (TargetTriple.getEnvironment() == llvm::Triple::GNUEABIHF ||
+        TargetTriple.getEnvironment() == llvm::Triple::MuslEABIHF) {
       TripleAliases.append(begin(ARMHFTriples), end(ARMHFTriples));
     } else {
       TripleAliases.append(begin(ARMTriples), end(ARMTriples));
     }
     break;
   case llvm::Triple::armeb:
   case llvm::Triple::thumbeb:
     LibDirs.append(begin(ARMebLibDirs), end(ARMebLibDirs));
-    if (TargetTriple.getEnvironment() == llvm::Triple::GNUEABIHF) {
+    if (TargetTriple.getEnvironment() == llvm::Triple::GNUEABIHF ||
+        TargetTriple.getEnvironment() == llvm::Triple::MuslEABIHF) {
       TripleAliases.append(begin(ARMebHFTriples), end(ARMebHFTriples));
     } else {
       TripleAliases.append(begin(ARMebTriples), end(ARMebTriples));
     }
     break;
   case llvm::Triple::x86_64:
     LibDirs.append(begin(X86_64LibDirs), end(X86_64LibDirs));
     TripleAliases.append(begin(X86_64Triples), end(X86_64Triples));

lib/Driver/ToolChains/Linux.cpp

default:
     break;
 
   // We use the existence of '/lib/<triple>' as a directory to detect some
   // common linux triples that don't quite match the Clang triple for both
   // 32-bit and 64-bit targets. Multiarch fixes its install triples to these
   // regardless of what the actual target triple is.
   case llvm::Triple::arm:
   case llvm::Triple::thumb:
-    if (TargetEnvironment == llvm::Triple::GNUEABIHF) {
+    if (TargetEnvironment == llvm::Triple::GNUEABIHF ||
+        TargetEnvironment == llvm::Triple::MuslEABIHF) {
       if (D.getVFS().exists(SysRoot + "/lib/arm-linux-gnueabihf"))
         return "arm-linux-gnueabihf";
     } else {
       if (D.getVFS().exists(SysRoot + "/lib/arm-linux-gnueabi"))
         return "arm-linux-gnueabi";
     }
     break;
   case llvm::Triple::armeb:
   case llvm::Triple::thumbeb:
-    if (TargetEnvironment == llvm::Triple::GNUEABIHF) {
+    if (TargetEnvironment == llvm::Triple::GNUEABIHF ||
+        TargetEnvironment == llvm::Triple::MuslEABIHF) {
       if (D.getVFS().exists(SysRoot + "/lib/armeb-linux-gnueabihf"))
         return "armeb-linux-gnueabihf";
     } else {
       if (D.getVFS().exists(SysRoot + "/lib/armeb-linux-gnueabi"))
         return "armeb-linux-gnueabi";
     }
     break;
   case llvm::Triple::x86: