[cc1as] Respect -mrelax-all

So that `clang -c -mrelax-all a.s` sets MCRelaxAll and assembles JMP/JCC
to a near jump instead of silently ignoring `-mrelax-all`.

Author: MaskRay

clang/test/Misc/cc1as-relax-all.s

@@ -0,0 +1,13 @@
+// REQUIRES: x86-registered-target
+// RUN: %clang -cc1as -triple x86_64 -filetype obj -mrelax-all %s -o %t.o
+// RUN: llvm-objdump -d %t.o | FileCheck %s
+
+// CHECK:      <.text>:
+// CHECK-NEXT:   0: e9 06 00 00 00                jmp     0xb <foo>
+// CHECK-NEXT:   5: 0f 84 00 00 00 00             je      0xb <foo>
+// CHECK-EMPTY:
+
+jmp foo
+je foo
+
+foo: ret

clang/tools/driver/cc1as_main.cpp

@@ -426,6 +426,7 @@ static bool ExecuteAssemblerImpl(AssemblerInvocation &Opts,
   assert(MRI && "Unable to create target register info!");
 
   MCTargetOptions MCOptions;
+  MCOptions.MCRelaxAll = Opts.RelaxAll;
   MCOptions.EmitDwarfUnwind = Opts.EmitDwarfUnwind;
   MCOptions.EmitCompactUnwindNonCanonical = Opts.EmitCompactUnwindNonCanonical;
   MCOptions.X86RelaxRelocations = Opts.RelaxELFRelocations;