[docs] Improve help for OpenMP options

[Hahnfeld]

Summary

• Add HelpText for -fopenmp so that it appears in clang --help.
• Hide -fno-openmp-simd, only list the positive option.
• Hide -fopenmp-relocatable-target and -fopenmp-use-tls from clang --help and from ClangCommandLineReference.
• Improve MetaVarName for -Xopenmp-target=<...>.

[ABataev]

1. Mark this patch as NFC.
2. LG

[gtbercea]

LG

cfe/trunk/include/clang/Driver/Options.td

def Xclang : Separate<["-"], "Xclang">,
   Flags<[DriverOption, CoreOption]>, Group<CompileOnly_Group>;
 def Xcuda_fatbinary : Separate<["-"], "Xcuda-fatbinary">,
   HelpText<"Pass <arg> to fatbinary invocation">, MetaVarName<"<arg>">;
 def Xcuda_ptxas : Separate<["-"], "Xcuda-ptxas">,
   HelpText<"Pass <arg> to the ptxas assembler">, MetaVarName<"<arg>">;
 def Xopenmp_target : Separate<["-"], "Xopenmp-target">,
   HelpText<"Pass <arg> to the target offloading toolchain.">, MetaVarName<"<arg>">;
 def Xopenmp_target_EQ : JoinedAndSeparate<["-"], "Xopenmp-target=">,
-  HelpText<"Pass <arg> to the specified target offloading toolchain. The triple that identifies the toolchain must be provided after the equals sign.">, MetaVarName<"<arg>">;
+  HelpText<"Pass <arg> to the target offloading toolchain identified by <triple>.">,
+  MetaVarName<"<triple> <arg>">;
 def z : Separate<["-"], "z">, Flags<[LinkerInput, RenderAsInput]>,
   HelpText<"Pass -z <arg> to the linker">, MetaVarName<"<arg>">,
   Group<Link_Group>;
 def Xlinker : Separate<["-"], "Xlinker">, Flags<[LinkerInput, RenderAsInput]>,
   HelpText<"Pass <arg> to the linker">, MetaVarName<"<arg>">,
   Group<Link_Group>;
 def Xpreprocessor : Separate<["-"], "Xpreprocessor">, Group<Preprocessor_Group>,
   HelpText<"Pass <arg> to the preprocessor">, MetaVarName<"<arg>">;
def fobjc_runtime_EQ : Joined<["-"], "fobjc-runtime=">, Group<f_Group>, Flags<[CC1Option]>,
   HelpText<"Specify the target Objective-C runtime kind and version">;
 def fobjc_abi_version_EQ : Joined<["-"], "fobjc-abi-version=">, Group<f_Group>;
 def fobjc_nonfragile_abi_version_EQ : Joined<["-"], "fobjc-nonfragile-abi-version=">, Group<f_Group>;
 def fobjc_nonfragile_abi : Flag<["-"], "fobjc-nonfragile-abi">, Group<f_Group>;
 def fno_objc_nonfragile_abi : Flag<["-"], "fno-objc-nonfragile-abi">, Group<f_Group>;
 
 def fobjc_sender_dependent_dispatch : Flag<["-"], "fobjc-sender-dependent-dispatch">, Group<f_Group>;
 def fomit_frame_pointer : Flag<["-"], "fomit-frame-pointer">, Group<f_Group>;
-def fopenmp : Flag<["-"], "fopenmp">, Group<f_Group>, Flags<[CC1Option, NoArgumentUnused]>;
+def fopenmp : Flag<["-"], "fopenmp">, Group<f_Group>, Flags<[CC1Option, NoArgumentUnused]>,
+  HelpText<"Parse OpenMP pragmas and generate parallel code.">;
 def fno_openmp : Flag<["-"], "fno-openmp">, Group<f_Group>, Flags<[NoArgumentUnused]>;
 def fopenmp_version_EQ : Joined<["-"], "fopenmp-version=">, Group<f_Group>, Flags<[CC1Option, NoArgumentUnused]>;
 def fopenmp_EQ : Joined<["-"], "fopenmp=">, Group<f_Group>;
-def fopenmp_use_tls : Flag<["-"], "fopenmp-use-tls">, Group<f_Group>, Flags<[NoArgumentUnused]>;
-def fnoopenmp_use_tls : Flag<["-"], "fnoopenmp-use-tls">, Group<f_Group>, Flags<[CC1Option, NoArgumentUnused]>;
+def fopenmp_use_tls : Flag<["-"], "fopenmp-use-tls">, Group<f_Group>,
+  Flags<[NoArgumentUnused, HelpHidden]>;
+def fnoopenmp_use_tls : Flag<["-"], "fnoopenmp-use-tls">, Group<f_Group>,
+  Flags<[CC1Option, NoArgumentUnused, HelpHidden]>;
 def fopenmp_targets_EQ : CommaJoined<["-"], "fopenmp-targets=">, Flags<[DriverOption, CC1Option]>,
   HelpText<"Specify comma-separated list of triples OpenMP offloading targets to be supported">;
-def fopenmp_dump_offload_linker_script : Flag<["-"], "fopenmp-dump-offload-linker-script">, Group<f_Group>,
-  Flags<[NoArgumentUnused]>;
-def fopenmp_relocatable_target : Flag<["-"], "fopenmp-relocatable-target">, Group<f_Group>, Flags<[CC1Option, NoArgumentUnused]>,
-  HelpText<"OpenMP target code is compiled as relocatable using the -c flag. For OpenMP targets the code is relocatable by default.">;
-def fnoopenmp_relocatable_target : Flag<["-"], "fnoopenmp-relocatable-target">, Group<f_Group>, Flags<[CC1Option, NoArgumentUnused]>,
-  HelpText<"Do not compile OpenMP target code as relocatable.">;
+def fopenmp_dump_offload_linker_script : Flag<["-"], "fopenmp-dump-offload-linker-script">,
+  Group<f_Group>, Flags<[NoArgumentUnused, HelpHidden]>;
+def fopenmp_relocatable_target : Flag<["-"], "fopenmp-relocatable-target">,
+  Group<f_Group>, Flags<[CC1Option, NoArgumentUnused, HelpHidden]>;
+def fnoopenmp_relocatable_target : Flag<["-"], "fnoopenmp-relocatable-target">,
+  Group<f_Group>, Flags<[CC1Option, NoArgumentUnused, HelpHidden]>;
 def fopenmp_simd : Flag<["-"], "fopenmp-simd">, Group<f_Group>, Flags<[CC1Option, NoArgumentUnused]>,
   HelpText<"Emit OpenMP code only for SIMD-based constructs.">;
-def fno_openmp_simd : Flag<["-"], "fno-openmp-simd">, Group<f_Group>, Flags<[CC1Option, NoArgumentUnused]>,
-  HelpText<"Disable OpenMP code for SIMD-based constructs.">;
+def fno_openmp_simd : Flag<["-"], "fno-openmp-simd">, Group<f_Group>, Flags<[CC1Option, NoArgumentUnused]>;
 def fno_optimize_sibling_calls : Flag<["-"], "fno-optimize-sibling-calls">, Group<f_Group>;
 def foptimize_sibling_calls : Flag<["-"], "foptimize-sibling-calls">, Group<f_Group>;
 def force__cpusubtype__ALL : Flag<["-"], "force_cpusubtype_ALL">;
 def force__flat__namespace : Flag<["-"], "force_flat_namespace">;
 def force__load : Separate<["-"], "force_load">;
 def force_addr : Joined<["-"], "fforce-addr">, Group<clang_ignored_f_Group>;
 def foutput_class_dir_EQ : Joined<["-"], "foutput-class-dir=">, Group<f_Group>;
 def fpack_struct : Flag<["-"], "fpack-struct">, Group<f_Group>;