[Driver,X86] Ignore -mfpmath= for assembler input

Some options are only claimed in AddX86TargetArgs/etc (called by
Clang::RenderTargetOptions).
For assembler input, `Add*TargetArgs` is not called. If an option is
unclaimed, it either leads to a -Wunused-command-line-argument warning
or an error (if `TargetSpecific` is set)
```
// clang '-###' --target=x86_64 -mfpmath=sse -c a.s
clang: error: unsupported option '-mfpmath=sse' for target 'x86_64'
```

For -mfpmath=, it's actually claimed by RenderFloatingPointOptions,
which should be moved to AddARMTargetArgs/AddX86TargetArgs later
(non-AArch32-non-x86 targets give a frontend error).
This change is localized and similar to D153691, for release/17.x
backporting.

Fix #65023

Reviewed By: thesamesam

Differential Revision: https://reviews.llvm.org/D159010

clang/lib/Driver/ToolChains/Arch/X86.cpp

@@ -118,7 +118,13 @@ std::string x86::getX86TargetCPU(const Driver &D, const ArgList &Args,
 
 void x86::getX86TargetFeatures(const Driver &D, const llvm::Triple &Triple,
                                const ArgList &Args,
-                               std::vector<StringRef> &Features) {
+                               std::vector<StringRef> &Features, bool ForAS) {
+  if (ForAS) {
+    // Some target-specific options are only handled in AddX86TargetArgs, which
+    // is not called by ClangAs::ConstructJob. Claim them here.
+    Args.claimAllArgs(options::OPT_mfpmath_EQ);
+  }
+
   // Claim and report unsupported -mabi=. Note: we don't support "sysv_abi" or
   // "ms_abi" as default function attributes.
   if (const Arg *A = Args.getLastArg(clang::driver::options::OPT_mabi_EQ)) {

clang/lib/Driver/ToolChains/Arch/X86.h

@@ -26,7 +26,7 @@ std::string getX86TargetCPU(const Driver &D, const llvm::opt::ArgList &Args,
 
 void getX86TargetFeatures(const Driver &D, const llvm::Triple &Triple,
                           const llvm::opt::ArgList &Args,
-                          std::vector<llvm::StringRef> &Features);
+                          std::vector<llvm::StringRef> &Features, bool ForAS);
 
 } // end namespace x86
 } // end namespace target

clang/lib/Driver/ToolChains/CommonArgs.cpp

@@ -528,7 +528,7 @@ void tools::getTargetFeatures(const Driver &D, const llvm::Triple &Triple,
     break;
   case llvm::Triple::x86:
   case llvm::Triple::x86_64:
-    x86::getX86TargetFeatures(D, Triple, Args, Features);
+    x86::getX86TargetFeatures(D, Triple, Args, Features, ForAS);
     break;
   case llvm::Triple::hexagon:
     hexagon::getHexagonTargetFeatures(D, Triple, Args, Features);

clang/test/Driver/x86-mfpmath.c

@@ -0,0 +1,5 @@
+// RUN: %clang -### -c --target=x86_64 -mfpmath=sse %s 2>&1 | FileCheck %s
+// CHECK: "-mfpmath" "sse"
+
+/// Don't warn for assembler input.
+// RUN: %clang -### -Werror -c --target=x86_64 -mfpmath=sse -x assembler %s 2>&1 | FileCheck /dev/null --implicit-check-not='"-mfpmath"'