[Driver] Accept -fno-lto in clang-cl

[aeubanks]

Summary

Some compiler-rt tests check for the presence of the compiler accepting
-fno-lto to add that flag. Otherwise some tests don't link due to
-flto mismatch between compiling and linking.

$ cmake ... -DLLVM_ENABLE_LTO=Thin ...
$ ninja projects/compiler-rt/lib/sanitizer_common/tests/Sanitizer-x86_64-Test.exe
previously failed, now links.

[hans]

lgtm

In general when -ffoo is supported by clang-cl, -fno-foo should be too, so this makes sense.

clang/include/clang/Driver/Options.td

def flax_vector_conversions : Flag<["-"], "flax-vector-conversions">, Group<f_Group>,
   Alias<flax_vector_conversions_EQ>, AliasArgs<["integer"]>;
 def flimited_precision_EQ : Joined<["-"], "flimited-precision=">, Group<f_Group>;
 def fapple_link_rtlib : Flag<["-"], "fapple-link-rtlib">, Group<f_Group>,
   HelpText<"Force linking the clang builtins runtime library">;
 def flto_EQ : Joined<["-"], "flto=">, Flags<[CoreOption, CC1Option]>, Group<f_Group>,
   HelpText<"Set LTO mode to either 'full' or 'thin'">, Values<"thin,full">;
 def flto : Flag<["-"], "flto">, Flags<[CoreOption, CC1Option]>, Group<f_Group>,
   HelpText<"Enable LTO in 'full' mode">;
-def fno_lto : Flag<["-"], "fno-lto">, Group<f_Group>,
+def fno_lto : Flag<["-"], "fno-lto">, Flags<[CoreOption, CC1Option]>, Group<f_Group>,
   HelpText<"Disable LTO mode (default)">;
 def flto_jobs_EQ : Joined<["-"], "flto-jobs=">,
   Flags<[CC1Option]>, Group<f_Group>,
   HelpText<"Controls the backend parallelism of -flto=thin (default "
            "of 0 means the number of threads will be derived from "
            "the number of CPUs detected)">;
 def fthinlto_index_EQ : Joined<["-"], "fthinlto-index=">,
   Flags<[CoreOption, CC1Option]>, Group<f_Group>,

clang/test/Driver/cl-options.c

 // RUN: env CL="/Gy" _CL_="/Gy- -- %s" %clang_cl -### 2>&1 | FileCheck -check-prefix=ENV-_CL_ %s
 // ENV-_CL_-NOT: "-ffunction-sections"
 
 // RUN: env CL="%s" _CL_="%s" not %clang --rsp-quoting=windows -c
 
 // RUN: %clang_cl -### /c -flto -- %s 2>&1 | FileCheck -check-prefix=LTO %s
 // LTO: -flto
 
+// RUN: %clang_cl -### /c -flto -fno-lto -- %s 2>&1 | FileCheck -check-prefix=LTO-NO %s
+// LTO-NO-NOT: "-flto"
+
 // RUN: %clang_cl -### /c -flto=thin -- %s 2>&1 | FileCheck -check-prefix=LTO-THIN %s
 // LTO-THIN: -flto=thin
 
 // RUN: %clang_cl -### -Fe%t.exe -entry:main -flto -- %s 2>&1 | FileCheck -check-prefix=LTO-WITHOUT-LLD %s
 // LTO-WITHOUT-LLD: LTO requires -fuse-ld=lld
 
 // RUN: %clang_cl  -### -- %s 2>&1 | FileCheck -check-prefix=NOCFGUARD %s
 // RUN: %clang_cl /guard:cf- -### -- %s 2>&1 | FileCheck -check-prefix=NOCFGUARD %s