BinUtils: Restore toolchain prefix detection from compiler name 'c++'

Since commit b12aec6c (BinUtils: prefer bin utils matching the
compiler version extension, 2020-12-11, v3.20.0-rc1~171^2) we recognize
`clangg++` and `g++` but not `c++`.  Restore `[gc]` in place of `g`
in the regex, as we had before that change.

Fixes: #22069

Modules/CMakeDetermineCXXCompiler.cmake

@@ -161,7 +161,7 @@ if (NOT _CMAKE_TOOLCHAIN_PREFIX)
 
   if("${CMAKE_CXX_COMPILER_ID}" MATCHES "GNU|Clang|QCC")
     get_filename_component(COMPILER_BASENAME "${CMAKE_CXX_COMPILER}" NAME)
-    if (COMPILER_BASENAME MATCHES "^(.+-)?(clang\\+\\+|g\\+\\+|clang-cl)(-[0-9]+(\\.[0-9]+)*)?(-[^.]+)?(\\.exe)?$")
+    if (COMPILER_BASENAME MATCHES "^(.+-)?(clang\\+\\+|[gc]\\+\\+|clang-cl)(-[0-9]+(\\.[0-9]+)*)?(-[^.]+)?(\\.exe)?$")
       set(_CMAKE_TOOLCHAIN_PREFIX ${CMAKE_MATCH_1})
       set(_CMAKE_TOOLCHAIN_SUFFIX ${CMAKE_MATCH_3})
       set(_CMAKE_COMPILER_SUFFIX ${CMAKE_MATCH_5})