[AIX] Emit error for -G option on AIX

1. Emit error for -G driver option on AIX
2. Adjust cmake file to use -Wl,-G instead of -G

On AIX, legacy XL compiler uses -G to produce a shared object enabled
for use with the run-time linker, which has different meanings from what
it is used for in Clang. And in Clang, other targets do not have -G map
to another functionality in their legacy compiler. So this error is more
important when we are on AIX.

Differential Revision: https://reviews.llvm.org/D89897

clang/lib/Driver/ToolChains/Clang.cpp

@@ -4958,6 +4958,11 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
   if (D.CCGenDiagnostics)
     CmdArgs.push_back("-disable-pragma-debug-crash");
 
+  if (RawTriple.isOSAIX())
+    if (Arg *A = Args.getLastArg(options::OPT_G))
+      D.Diag(diag::err_drv_unsupported_opt_for_target)
+          << A->getSpelling() << RawTriple.str();
+
   bool UseSeparateSections = isUseSeparateSections(Triple);
 
   if (Args.hasFlag(options::OPT_ffunction_sections,

clang/test/Driver/aix-err-options.c

@@ -0,0 +1,7 @@
+// RUN: %clang -target powerpc32-ibm-aix-xcoff -### -S -emit-llvm -G 0 2>&1 %s | \
+// RUN:   FileCheck --check-prefix=CHECK32 %s
+// RUN: %clang -target powerpc64-ibm-aix-xcoff -### -S -emit-llvm -G 0 2>&1 %s | \
+// RUN:   FileCheck --check-prefix=CHECK64 %s
+
+// CHECK32: error: unsupported option '-G' for target 'powerpc32-ibm-aix-xcoff'
+// CHECK64: error: unsupported option '-G' for target 'powerpc64-ibm-aix-xcoff'

llvm/CMakeLists.txt

@@ -930,7 +930,7 @@ if (UNIX AND ${CMAKE_SYSTEM_NAME} MATCHES "AIX")
 
   # Modules should be built with -G, so we can use runtime linking with
   # plugins.
-  string(APPEND CMAKE_MODULE_LINKER_FLAGS " -G")
+  string(APPEND CMAKE_MODULE_LINKER_FLAGS " -Wl,-G")
 
   # Also set the correct flags for building shared libraries.
   string(APPEND CMAKE_SHARED_LINKER_FLAGS " -shared")