clang-cl: Accept MSVC 2015's `/execution-charset:utf-8` flag.

[thakis]

Summary

Like https://reviews.llvm.org/D23807, but for execution-charset.

[thakis]

;-;

[thakis]

!!

[majnemer]

lib/Driver/Tools.cpp

5838–5846

I'd use compare_lower because lower introduces a std::string.

[hans]

lgtm

majnemer's suggestion sounds good though, and for inputCharset too.

[thakis]

r279866, thanks!

include/clang/Driver/CLCompatOptions.td

def _SLASH_Qvec : CLFlag<"Qvec">,
   HelpText<"Enable the loop vectorization passes">, Alias<fvectorize>;
 def _SLASH_Qvec_ : CLFlag<"Qvec-">,
   HelpText<"Disable the loop vectorization passes">, Alias<fno_vectorize>;
 def _SLASH_showIncludes : CLFlag<"showIncludes">,
   HelpText<"Print info about included files to stderr">,
   Alias<show_includes>;
 def _SLASH_source_charset : CLCompileJoined<"source-charset:">,
   HelpText<"Source encoding, supports only UTF-8">, Alias<finput_charset_EQ>;
+def _SLASH_execution_charset : CLCompileJoined<"execution-charset:">,
+  HelpText<"Runtime encoding, supports only UTF-8">, Alias<fexec_charset_EQ>;
 def _SLASH_std : CLCompileJoined<"std:">,
   HelpText<"Language standard to compile for">;
 def _SLASH_U : CLJoinedOrSeparate<"U">, HelpText<"Undefine macro">,
   MetaVarName<"<macro>">, Alias<U>;
 def _SLASH_W0 : CLFlag<"W0">, HelpText<"Disable all warnings">, Alias<w>;
 def _SLASH_W1 : CLFlag<"W1">, HelpText<"Enable -Wall">, Alias<Wall>;
 def _SLASH_W2 : CLFlag<"W2">, HelpText<"Enable -Wall">, Alias<Wall>;
 def _SLASH_W3 : CLFlag<"W3">, HelpText<"Enable -Wall">, Alias<Wall>;

lib/Driver/Tools.cpp

   // -fsigned-bitfields is default, and clang doesn't support -fno-for-scope.
   if (!Args.hasFlag(options::OPT_ffor_scope, options::OPT_fno_for_scope))
     D.Diag(diag::err_drv_clang_unsupported)
         << Args.getLastArg(options::OPT_fno_for_scope)->getAsString(Args);
 
   // -finput_charset=UTF-8 is default. Reject others
   if (Arg *inputCharset = Args.getLastArg(options::OPT_finput_charset_EQ)) {
     StringRef value = inputCharset->getValue();
     if (value.lower() != "utf-8")
       D.Diag(diag::err_drv_invalid_value) << inputCharset->getAsString(Args)
                                           << value;
   }
 
   // -fexec_charset=UTF-8 is default. Reject others
   if (Arg *execCharset = Args.getLastArg(options::OPT_fexec_charset_EQ)) {
     StringRef value = execCharset->getValue();
-    if (value != "UTF-8")
+    if (value.lower() != "utf-8")
       D.Diag(diag::err_drv_invalid_value) << execCharset->getAsString(Args)
                                           << value;
   }
 
   // -fcaret-diagnostics is default.
   if (!Args.hasFlag(options::OPT_fcaret_diagnostics,
                     options::OPT_fno_caret_diagnostics, true))
     CmdArgs.push_back("-fno-caret-diagnostics");

test/Driver/cl-options.c

 // RUN: %clang_cl /E /showIncludes -### -- %s 2>&1 | FileCheck -check-prefix=showIncludes_E %s
 // RUN: %clang_cl /EP /showIncludes -### -- %s 2>&1 | FileCheck -check-prefix=showIncludes_E %s
 // showIncludes_E: warning: argument unused during compilation: '--show-includes'
 
 // /source-charset: should warn on everything except UTF-8.
 // RUN: %clang_cl /source-charset:utf-16 -### -- %s 2>&1 | FileCheck -check-prefix=source-charset-utf-16 %s
 // source-charset-utf-16: invalid value 'utf-16'
 
+// /execution-charset: should warn on everything except UTF-8.
+// RUN: %clang_cl /execution-charset:utf-16 -### -- %s 2>&1 | FileCheck -check-prefix=execution-charset-utf-16 %s
+// execution-charset-utf-16: invalid value 'utf-16'
+//
 // RUN: %clang_cl /Umymacro -### -- %s 2>&1 | FileCheck -check-prefix=U %s
 // RUN: %clang_cl /U mymacro -### -- %s 2>&1 | FileCheck -check-prefix=U %s
 // U: "-U" "mymacro"
 
 // RUN: %clang_cl /vd2 -### -- %s 2>&1 | FileCheck -check-prefix=VD2 %s
 // VD2: -vtordisp-mode=2
 
 // RUN: %clang_cl /vmg -### -- %s 2>&1 | FileCheck -check-prefix=VMG %s

 // RUN: %clang_cl /c \
 // RUN:    /analyze- \
 // RUN:    /bigobj \
 // RUN:    /cgthreads4 \
 // RUN:    /cgthreads8 \
 // RUN:    /d2FastFail \
 // RUN:    /d2Zi+ \
 // RUN:    /errorReport:foo \
+// RUN:    /execution-charset:utf-8 \
 // RUN:    /FC \
 // RUN:    /Fdfoo \
 // RUN:    /FS \
 // RUN:    /Gd \
 // RUN:    /GF \
 // RUN:    /GS- \
 // RUN:    /kernel- \
 // RUN:    /nologo \