Add explicit architecture flag behavior testing

Author: ericastor

llvm/test/tools/llvm-ml/architecture.asm

@@ -0,0 +1,9 @@
+; RUN: llvm-ml64 -filetype=s %s /Fo - | FileCheck %s --implicit-check-not=error:
+; RUN: llvm-ml -m64 -filetype=s %s /Fo - | FileCheck %s --implicit-check-not=error:
+
+.code
+
+xor rax, rax
+; CHECK: xor rax, rax
+
+end

llvm/test/tools/llvm-ml/architecture_errors.asm

@@ -0,0 +1,10 @@
+; RUN: not llvm-ml -filetype=s %s /Fo - 2>&1 | FileCheck %s
+; RUN: not llvm-ml -m32 -filetype=s %s /Fo - 2>&1 | FileCheck %s
+; RUN: not llvm-ml64 -m32 -filetype=s %s /Fo - 2>&1 | FileCheck %s
+
+.code
+
+; CHECK: :[[# @LINE + 1]]:5: error: register %rax is only available in 64-bit mode
+xor rax, rax
+
+end

utils/bazel/llvm-project-overlay/llvm/BUILD.bazel

@@ -5116,6 +5116,14 @@ llvm_driver_cc_binary(
     deps = [":llvm-ml-lib"],
 )
 
+genrule(
+    name = "gen_llvm-ml64",
+    srcs = [":llvm-ml"],
+    outs = ["llvm-ml64"],
+    cmd = "ln -sf $$(basename $<) $@",
+    output_to_bindir = 1,
+)
+
 cc_binary(
     name = "llvm-modextract",
     srcs = glob([