From Brett Viren:

fix gcc version detection.


git-svn-id: http://root.cern.ch/svn/root/trunk@44252 27541ba8-7e3a-0410-8455-c3a389f83636

cmake/modules/CheckCompiler.cmake

@@ -25,9 +25,19 @@ endif()
 #---Obtain the major and minor version of the GNU compiler-------------------------------------------
 if (CMAKE_COMPILER_IS_GNUCXX)
   exec_program(${CMAKE_C_COMPILER} ARGS "-dumpversion" OUTPUT_VARIABLE _gcc_version_info)
-  string(REGEX REPLACE "^([0-9]+)\\.([0-9]+)\\.?([0-9])?" "\\1" GCC_MAJOR "${_gcc_version_info}")
-  string(REGEX REPLACE "^([0-9]+)\\.([0-9]+)\\.?([0-9])?" "\\2" GCC_MINOR "${_gcc_version_info}")
-  string(REGEX REPLACE "^([0-9]+)\\.([0-9]+)\\.?([0-9])?" "\\3" GCC_PATCH "${_gcc_version_info}")
+  string(REGEX REPLACE "^([0-9]+).*$"                   "\\1" GCC_MAJOR ${_gcc_version_info})
+  string(REGEX REPLACE "^[0-9]+\\.([0-9]+).*$"          "\\1" GCC_MINOR ${_gcc_version_info})
+  string(REGEX REPLACE "^[0-9]+\\.[0-9]+\\.([0-9]+).*$" "\\1" GCC_PATCH ${_gcc_version_info})
+
+  if(GCC_PATCH MATCHES "\\.+")
+    set(GCC_PATCH "")
+  endif()
+  if(GCC_MINOR MATCHES "\\.+")
+    set(GCC_MINOR "")
+  endif()
+  if(GCC_MAJOR MATCHES "\\.+")
+    set(GCC_MAJOR "")
+  endif()
   message(STATUS "Found GCC. Major version ${GCC_MAJOR}, minor version ${GCC_MINOR}")
   set(COMPILER_VERSION gcc${GCC_MAJOR}${GCC_MINOR}${GCC_PATCH})
 else()