[Driver] Ignore -fno-semantic-interposition

[MaskRay]

Summary

Fedora wants to build projects with -fno-semantic-interposition (e.g.
https://fedoraproject.org/wiki/Changes/PythonNoSemanticInterpositionSpeedup),
which is supported by GCC>=5.

Clang's current behavior is similar to -fno-semantic-interposition and
the end goal is to make it more so
(https://lists.llvm.org/pipermail/llvm-dev/2016-November/107625.html).
Ignore this option.

We should let users know -fsemantic-interposition is not currently
supported, so it should remain a hard error.

[merge_guards_bot]

Unit tests: pass. 61849 tests passed, 0 failed and 781 were skipped.

clang-tidy: unknown.

clang-format: pass.

Build artifacts: diff.json, clang-format.patch, CMakeCache.txt, console-log.txt, test-results.xml

[serge-sans-paille]

LGTM

[MaskRay]

Use Flag<> instead

[MaskRay]

In D72724#1820362, @serge-sans-paille wrote:

LGTM

I don't follow Fedora news. It is just that a friend informed me of this -fno-semantic-interposition movement two days ago and I postulated that it was your motivation to ping that patch...

[serge-sans-paille]

@MaskRay: is that okay with you if I start implementing -fsemantic-interposition based on dso_preemptable?

[merge_guards_bot]

Unit tests: pass. 61856 tests passed, 0 failed and 781 were skipped.

clang-tidy: unknown.

clang-format: pass.

Build artifacts: diff.json, clang-format.patch, CMakeCache.txt, console-log.txt, test-results.xml

[MaskRay]

In D72724#1820392, @serge-sans-paille wrote:

@MaskRay: is that okay with you if I start implementing -fsemantic-interposition based on dso_preemptable?

I haven't done anything in this area. Go ahead:) I'd like to help or review if you need anything from me.

[MaskRay]

Ah, I'll want to figure out how to emit local aliases to dso_local as a follow-up of D72197, but that should be orthogonal to what you want to do.

clang/include/clang/Driver/Options.td

defm inline_functions_called_once : BooleanFFlag<"inline-functions-called-once">,
     Group<clang_ignored_gcc_optimization_f_Group>;
 def finline_limit_EQ : Joined<["-"], "finline-limit=">, Group<clang_ignored_gcc_optimization_f_Group>;
 defm finline_limit : BooleanFFlag<"inline-limit">, Group<clang_ignored_gcc_optimization_f_Group>;
 defm inline_small_functions : BooleanFFlag<"inline-small-functions">,
     Group<clang_ignored_gcc_optimization_f_Group>;
 defm ipa_cp : BooleanFFlag<"ipa-cp">,
     Group<clang_ignored_gcc_optimization_f_Group>;
 defm ivopts : BooleanFFlag<"ivopts">, Group<clang_ignored_gcc_optimization_f_Group>;
+def : Flag<["-"], "fno-semantic-interposition">, Group<clang_ignored_f_Group>;
 defm non_call_exceptions : BooleanFFlag<"non-call-exceptions">, Group<clang_ignored_f_Group>;
 defm peel_loops : BooleanFFlag<"peel-loops">, Group<clang_ignored_gcc_optimization_f_Group>;
 defm permissive : BooleanFFlag<"permissive">, Group<clang_ignored_f_Group>;
 defm prefetch_loop_arrays : BooleanFFlag<"prefetch-loop-arrays">, Group<clang_ignored_gcc_optimization_f_Group>;
 defm printf : BooleanFFlag<"printf">, Group<clang_ignored_f_Group>;
 defm profile : BooleanFFlag<"profile">, Group<clang_ignored_f_Group>;
 defm profile_correction : BooleanFFlag<"profile-correction">, Group<clang_ignored_gcc_optimization_f_Group>;
 defm profile_generate_sampling : BooleanFFlag<"profile-generate-sampling">, Group<clang_ignored_f_Group>;

clang/test/Driver/clang_f_opts.c

 // RUN:     -feliminate-unused-debug-types -fno-eliminate-unused-debug-types  \
 // RUN:     -fgcse -fno-gcse                                                  \
 // RUN:     -fident -fno-ident                                                \
 // RUN:     -fimplicit-templates -fno-implicit-templates                      \
 // RUN:     -finput-charset=UTF-8                                             \
 // RUN:     -fexec-charset=UTF-8                                             \
 // RUN:     -fivopts -fno-ivopts                                              \
 // RUN:     -fnon-call-exceptions -fno-non-call-exceptions                    \
+// RUN:     -fno-semantic-interposition                                       \
 // RUN:     -fpermissive -fno-permissive                                      \
 // RUN:     -fdefer-pop -fno-defer-pop                                        \
 // RUN:     -fprefetch-loop-arrays -fno-prefetch-loop-arrays                  \
 // RUN:     -fprofile-correction -fno-profile-correction                      \
 // RUN:     -fprofile-values -fno-profile-values                              \
 // RUN:     -frounding-math -fno-rounding-math                                \
 // RUN:     -fsee -fno-see                                                    \
 // RUN:     -ftracer -fno-tracer                                              \