[Driver] Make "-fno-split-machine-functions" a valid flag for all archs

Previously, clang reports an error when -fno-split-machine-functions
is used for non-X86 archs.

However, in some cases, users may specify flags as
"-fsplit-machine-functions -fother-flags
-fno-split-machine-functions", the first one is from a global flag
set, the last one is used to negate the global flag, we think this is
a valid usage mode.

Another cases is when clang is used to invoke multiple workloads, like
"-x cuda -fsplit-machine-functions -Xarch_device
-fno-split-machine-functions", the latter is used to negate
-fsplit-machine-functions when invoke workloads for GPU."

This change makes this work.

Reviewed By: maskray

Differential Revision: https://reviews.llvm.org/D158755

clang/lib/Driver/ToolChains/Clang.cpp

@@ -5872,13 +5872,13 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
 
   if (Arg *A = Args.getLastArg(options::OPT_fsplit_machine_functions,
                                options::OPT_fno_split_machine_functions)) {
-    // This codegen pass is only available on x86-elf targets.
-    if (Triple.isX86() && Triple.isOSBinFormatELF()) {
-      if (A->getOption().matches(options::OPT_fsplit_machine_functions))
+    if (!A->getOption().matches(options::OPT_fno_split_machine_functions)) {
+      // This codegen pass is only available on x86-elf targets.
+      if (Triple.isX86() && Triple.isOSBinFormatELF())
         A->render(Args, CmdArgs);
-    } else {
-      D.Diag(diag::err_drv_unsupported_opt_for_target)
-          << A->getAsString(Args) << TripleStr;
+      else
+        D.Diag(diag::err_drv_unsupported_opt_for_target)
+            << A->getAsString(Args) << TripleStr;
     }
   }
 

clang/test/Driver/fsplit-machine-functions.c

@@ -15,6 +15,4 @@
 // RUN: not %clang -### -c --target=arm-unknown-linux -fsplit-machine-functions %s 2>&1 | FileCheck %s --check-prefix=ERR
 // ERR: error: unsupported option '-fsplit-machine-functions' for target
 
-/// FIXME
-// RUN: not %clang -### -c --target=arm-unknown-linux -fsplit-machine-functions -fno-split-machine-functions %s 2>&1 | FileCheck %s --check-prefix=ERR2
-// ERR2: error: unsupported option '-fno-split-machine-functions' for target
+// RUN: %clang -### --target=arm-unknown-linux -fsplit-machine-functions -fno-split-machine-functions %s