Add a ENABLE_X86_RELAX_RELOCATIONS  cmake option.

This corresponds to binutils' --enable-x86-relax-relocations.

llvm-svn: 273224
diff --git a/clang/lib/Driver/Tools.cpp b/clang/lib/Driver/Tools.cpp
index a23f660..c0d6c52 100644
--- a/clang/lib/Driver/Tools.cpp
+++ b/clang/lib/Driver/Tools.cpp
@@ -2839,7 +2839,7 @@
   // options.
   bool CompressDebugSections = false;
 
-  bool UseRelaxRelocations = false;
+  bool UseRelaxRelocations = ENABLE_X86_RELAX_RELOCATIONS;
   const char *MipsTargetFeature = nullptr;
   for (const Arg *A :
        Args.filtered(options::OPT_Wa_COMMA, options::OPT_Xassembler)) {