[libcxx] Fix wrong messages of git version

[sunshaoce]

ping

[ldionne]

Is there a reason why we're not fixing this upstream in GoogleBenchmark instead?

third-party/benchmark/cmake/GetGitVersion.cmake

 
 if(__get_git_version)
   return()
 endif()
 set(__get_git_version INCLUDED)
 
 function(get_git_version var)
   if(GIT_EXECUTABLE)
-      execute_process(COMMAND ${GIT_EXECUTABLE} describe --tags --match "v[0-9]*.[0-9]*.[0-9]*" --abbrev=8
+      execute_process(COMMAND ${GIT_EXECUTABLE} describe --tags --match "llvmorg-[0-9]*.[0-9]*.[0-9]*" --abbrev=8
           WORKING_DIRECTORY ${PROJECT_SOURCE_DIR}
           RESULT_VARIABLE status
           OUTPUT_VARIABLE GIT_DESCRIBE_VERSION
           ERROR_QUIET)
       if(status)
           set(GIT_DESCRIBE_VERSION "v0.0.0")
       endif()
       
       string(STRIP ${GIT_DESCRIBE_VERSION} GIT_DESCRIBE_VERSION)
-      if(GIT_DESCRIBE_VERSION MATCHES v[^-]*-) 
-         string(REGEX REPLACE "v([^-]*)-([0-9]+)-.*" "\\1.\\2"  GIT_VERSION ${GIT_DESCRIBE_VERSION})
-      else()
-         string(REGEX REPLACE "v(.*)" "\\1" GIT_VERSION ${GIT_DESCRIBE_VERSION})
-      endif()
+      string(REGEX REPLACE "llvmorg-(.*)" "v\\1"  GIT_VERSION ${GIT_DESCRIBE_VERSION})
 
       # Work out if the repository is dirty
       execute_process(COMMAND ${GIT_EXECUTABLE} update-index -q --refresh
           WORKING_DIRECTORY ${PROJECT_SOURCE_DIR}
           OUTPUT_QUIET
           ERROR_QUIET)
       execute_process(COMMAND ${GIT_EXECUTABLE} diff-index --name-only HEAD --
           WORKING_DIRECTORY ${PROJECT_SOURCE_DIR}
           OUTPUT_VARIABLE GIT_DIFF_INDEX
           ERROR_QUIET)
       string(COMPARE NOTEQUAL "${GIT_DIFF_INDEX}" "" GIT_DIRTY)
       if (${GIT_DIRTY})
           set(GIT_DESCRIBE_VERSION "${GIT_DESCRIBE_VERSION}-dirty")
       endif()
-      message(STATUS "git version: ${GIT_DESCRIBE_VERSION} normalized to ${GIT_VERSION}")
+      message(STATUS "Git version: ${GIT_DESCRIBE_VERSION} normalized to ${GIT_VERSION}")
   else()
       set(GIT_VERSION "0.0.0")
   endif()
 
   set(${var} ${GIT_VERSION} PARENT_SCOPE)
 endfunction()