Eclipse: fix #13313, always set LANG to C, also if unset

Otherwise include dir detection does not work with MinGW on french systems.

Alex

Modules/CMakeExtraGeneratorDetermineCompilerMacrosAndIncludeDirs.cmake

@@ -80,15 +80,10 @@ ENDMACRO(_DETERMINE_GCC_SYSTEM_INCLUDE_DIRS _lang)
 SET(_orig_lc_all      $ENV{LC_ALL})
 SET(_orig_lc_messages $ENV{LC_MESSAGES})
 SET(_orig_lang        $ENV{LANG})
-IF(_orig_lc_all)
-  SET(ENV{LC_ALL}      C)
-ENDIF()
-IF(_orig_lc_messages)
-  SET(ENV{LC_MESSAGES} C)
-ENDIF()
-IF(_orig_lang)
-  SET(ENV{LANG}        C)
-ENDIF()
+
+SET(ENV{LC_ALL}      C)
+SET(ENV{LC_MESSAGES} C)
+SET(ENV{LANG}        C)
 
 # Now check for C, works for gcc and Intel compiler at least
 IF (NOT CMAKE_EXTRA_GENERATOR_C_SYSTEM_INCLUDE_DIRS)
@@ -109,12 +104,6 @@ IF (NOT CMAKE_EXTRA_GENERATOR_CXX_SYSTEM_INCLUDE_DIRS)
 ENDIF ()
 
 # Restore original LC_ALL, LC_MESSAGES, and LANG
-IF(_orig_lc_all)
-  SET(ENV{LC_ALL}      ${_orig_lc_all})
-ENDIF()
-IF(_orig_lc_messages)
-  SET(ENV{LC_MESSAGES} ${_orig_lc_messages})
-ENDIF()
-IF(_orig_lang)
-  SET(ENV{LANG}        ${_orig_lang})
-ENDIF()
+SET(ENV{LC_ALL}      ${_orig_lc_all})
+SET(ENV{LC_MESSAGES} ${_orig_lc_messages})
+SET(ENV{LANG}        ${_orig_lang})