[AIX][Clang][Driver] Add handling of nostartfiles option

[jasonliu]

LGTM.

clang/lib/Driver/ToolChains/AIX.cpp

if (Args.hasArg(options::OPT_pg))
       return IsArch32Bit ? "gcrt0.o" : "gcrt0_64.o";
     // Enable profiling when "-p" is specified.
     else if (Args.hasArg(options::OPT_p))
       return IsArch32Bit ? "mcrt0.o" : "mcrt0_64.o";
     else
       return IsArch32Bit ? "crt0.o" : "crt0_64.o";
   };
 
-  if (!Args.hasArg(options::OPT_nostdlib)) {
+  if (!Args.hasArg(options::OPT_nostdlib, options::OPT_nostartfiles)) {
     CmdArgs.push_back(
         Args.MakeArgString(ToolChain.GetFilePath(getCrt0Basename())));
   }
 
   // Collect all static constructor and destructor functions in CXX mode. This
   // has to come before AddLinkerInputs as the implied option needs to precede
   // any other '-bcdtors' settings or '-bnocdtors' that '-Wl' might forward.
   if (D.CCCIsCXX())

clang/test/Driver/aix-ld.c

 // CHECK-LD64-NOSTDLIBXX-LCXX:     "{{.*}}ld{{(.exe)?}}"
 // CHECK-LD64-NOSTDLIBXX-LCXX:     "-b64"
 // CHECK-LD64-NOSTDLIBXX-LCXX:     "-bpT:0x100000000" "-bpD:0x110000000"
 // CHECK-LD64-NOSTDLIBXX-LCXX:     "[[SYSROOT]]/usr/lib{{/|\\\\}}crt0_64.o"
 // CHECK-LD64-NOSTDLIBXX-LCXX:     "-L[[SYSROOT]]/usr/lib"
 // CHECK-LD64-NOSTDLIBXX-LCXX-NOT: "-lc++"
 // CHECK-LD64-NOSTDLIBXX-LCXX:     "-lc"
 
+// Check powerpc64-ibm-aix7.1.0.0, 32-bit. -nostartfiles.
+// RUN: %clangxx -no-canonical-prefixes %s 2>&1 -### \
+// RUN:        -nostartfiles \
+// RUN:        -target powerpc-ibm-aix7.1.0.0 \
+// RUN:        --sysroot %S/Inputs/aix_ppc_tree \
+// RUN:   | FileCheck --check-prefix=CHECK-LD32-NOSTARTFILES-LCXX %s
+// CHECK-LD32-NOSTARTFILES-LCXX:     {{.*}}clang{{.*}}" "-cc1" "-triple" "powerpc-ibm-aix7.1.0.0"
+// CHECK-LD32-NOSTARTFILES-LCXX:     "-isysroot" "[[SYSROOT:[^"]+]]"
+// CHECK-LD32-NOSTARTFILES-LCXX:     "{{.*}}ld{{(.exe)?}}"
+// CHECK-LD32-NOSTARTFILES-LCXX:     "-b32"
+// CHECK-LD32-NOSTARTFILES-LCXX:     "-bpT:0x10000000" "-bpD:0x20000000"
+// CHECK-LD32-NOSTARTFILES-LCXX-NOT: "[[SYSROOT]]/usr/lib{{/|\\\\}}crt0.o"
+// CHECK-LD32-NOSTARTFILES-LCXX:     "-L[[SYSROOT]]/usr/lib"
+// CHECK-LD32-NOSTARTFILES-LCXX      "-lc++"
+// CHECK-LD32-NOSTARTFILES-LCXX:     "-lc"
+
+// Check powerpc64-ibm-aix7.1.0.0, 64-bit. -nostartfiles.
+// RUN: %clangxx -no-canonical-prefixes %s 2>&1 -### \
+// RUN:        -nostartfiles \
+// RUN:        -target powerpc-ibm-aix7.1.0.0 \
+// RUN:        --sysroot %S/Inputs/aix_ppc_tree \
+// RUN:   | FileCheck --check-prefix=CHECK-LD32-NOSTARTFILES-LCXX %s
+// CHECK-LD64-NOSTARTFILES-LCXX:     {{.*}}clang{{.*}}" "-cc1" "-triple" "powerpc64-ibm-aix7.1.0.0"
+// CHECK-LD64-NOSTARTFILES-LCXX:     "-isysroot" "[[SYSROOT:[^"]+]]"
+// CHECK-LD64-NOSTARTFILES-LCXX:     "{{.*}}ld{{(.exe)?}}"
+// CHECK-LD64-NOSTARTFILES-LCXX:     "-b64"
+// CHECK-LD64-NOSTARTFILES-LCXX:     "-bpT:0x100000000" "-bpD:0x110000000"
+// CHECK-LD64-NOSTARTFILES-LCXX-NOT: "[[SYSROOT]]/usr/lib{{/|\\\\}}crt0_64.o"
+// CHECK-LD64-NOSTARTFILES-LCXX:     "-L[[SYSROOT]]/usr/lib"
+// CHECK-LD64-NOSTARTFILES-LCXX:     "-lc++"
+// CHECK-LD64-NOSTARTFILES-LCXX:     "-lc"
+
 // Check powerpc-ibm-aix7.1.0.0, 32-bit. -stdlib=libstdc++ invokes fatal error.
 // RUN: not --crash %clangxx -no-canonical-prefixes %s 2>&1 -### \
 // RUN:        -target powerpc-ibm-aix7.1.0.0 \
 // RUN:        -stdlib=libstdc++ \
 // RUN:        --sysroot %S/Inputs/aix_ppc_tree \
 // RUN:   | FileCheck --check-prefix=CHECK-LD-LIBSTDCXX %s
 
 // Check powerpc64-ibm-aix7.1.0.0, 64-bit. -stdlib=libstdc++ invokes fatal error.
 // RUN: not --crash %clangxx -no-canonical-prefixes %s 2>&1 -### \
 // RUN:        -target powerpc64-ibm-aix7.1.0.0 \
 // RUN:        -stdlib=libstdc++ \
 // RUN:        --sysroot %S/Inputs/aix_ppc_tree \
 // RUN:   | FileCheck --check-prefix=CHECK-LD-LIBSTDCXX %s
 // CHECK-LD-LIBSTDCXX: LLVM ERROR: linking libstdc++ unimplemented on AIX