[flang][driver] Avoid mentions of Clang in Flang's command line reference. (#88932)

The help text was not updated in #87360.

Clang is also mentioned for the diagnostic warnings reference, which
mostly applies to C/C++/Obj-C, not Fortran. #81726 already tried to fix
this, and I don't know a better solution.

Author: Meinersbur

clang/include/clang/Driver/Options.td

@@ -807,8 +807,12 @@ def gcc_install_dir_EQ : Joined<["--"], "gcc-install-dir=">,
   "Note: executables (e.g. ld) used by the compiler are not overridden by the selected GCC installation">;
 def gcc_toolchain : Joined<["--"], "gcc-toolchain=">, Flags<[NoXarchOption]>,
   Visibility<[ClangOption, FlangOption]>,
-  HelpText<"Specify a directory where Clang can find 'include' and 'lib{,32,64}/gcc{,-cross}/$triple/$version'. "
-  "Clang will use the GCC installation with the largest version">;
+  HelpText<
+    "Specify a directory where Clang can find 'include' and 'lib{,32,64}/gcc{,-cross}/$triple/$version'. "
+    "Clang will use the GCC installation with the largest version">,
+  HelpTextForVariants<[FlangOption],
+    "Specify a directory where Flang can find 'lib{,32,64}/gcc{,-cross}/$triple/$version'. "
+    "Flang will use the GCC installation with the largest version">;
 def gcc_triple_EQ : Joined<["--"], "gcc-triple=">,
   HelpText<"Search for the GCC installation with the specified triple.">;
 def CC : Flag<["-"], "CC">, Visibility<[ClangOption, CC1Option]>,

flang/test/Driver/driver-help-hidden.f90

@@ -109,7 +109,7 @@
 ! CHECK-NEXT: -fxor-operator          Enable .XOR. as a synonym of .NEQV.
 ! CHECK-NEXT: --gcc-install-dir=<value>
 ! CHECK-NEXT:                         Use GCC installation in the specified directory. The directory ends with path components like 'lib{,32,64}/gcc{,-cross}/$triple/$version'. Note: executables (e.g. ld) used by the compiler are not overridden by the selected GCC installation
-! CHECK-NEXT: --gcc-toolchain=<value> Specify a directory where Clang can find 'include' and 'lib{,32,64}/gcc{,-cross}/$triple/$version'. Clang will use the GCC installation with the largest version
+! CHECK-NEXT: --gcc-toolchain=<value> Specify a directory where Flang can find 'lib{,32,64}/gcc{,-cross}/$triple/$version'. Flang will use the GCC installation with the largest version
 ! CHECK-NEXT: -gline-directives-only  Emit debug line info directives only
 ! CHECK-NEXT: -gline-tables-only      Emit debug line number tables only
 ! CHECK-NEXT: -gpulibc                Link the LLVM C Library for GPUs

flang/test/Driver/driver-help.f90

@@ -97,7 +97,7 @@
 ! HELP-NEXT: -fxor-operator          Enable .XOR. as a synonym of .NEQV.
 ! HELP-NEXT: --gcc-install-dir=<value>
 ! HELP-NEXT:                         Use GCC installation in the specified directory. The directory ends with path components like 'lib{,32,64}/gcc{,-cross}/$triple/$version'. Note: executables (e.g. ld) used by the compiler are not overridden by the selected GCC installation
-! HELP-NEXT: --gcc-toolchain=<value> Specify a directory where Clang can find 'include' and 'lib{,32,64}/gcc{,-cross}/$triple/$version'. Clang will use the GCC installation with the largest version
+! HELP-NEXT: --gcc-toolchain=<value> Specify a directory where Flang can find 'lib{,32,64}/gcc{,-cross}/$triple/$version'. Flang will use the GCC installation with the largest version
 ! HELP-NEXT: -gline-directives-only  Emit debug line info directives only
 ! HELP-NEXT: -gline-tables-only      Emit debug line number tables only
 ! HELP-NEXT: -gpulibc                Link the LLVM C Library for GPUs