Factor AIX and XL compiler flags into common module

Factor duplicate flag information from Platform/AIX-XL-*.cmake into
Platform/AIX-XL.cmake and load it from the original files.

Modules/Platform/AIX-XL-C.cmake

@@ -1,4 +1,2 @@
-SET(CMAKE_SHARED_LIBRARY_CREATE_C_FLAGS "-G -Wl,-brtl,-bnoipath")  # -shared
-SET(CMAKE_SHARED_LIBRARY_LINK_C_FLAGS "-Wl,-brtl,-bnoipath,-bexpall")  # +s, flag for exe link to use shared lib
-SET(CMAKE_SHARED_LIBRARY_C_FLAGS " ")
-SET(CMAKE_SHARED_MODULE_C_FLAGS  " ")
+include(Platform/AIX-XL)
+__aix_compiler_xl(C)

Modules/Platform/AIX-XL-CXX.cmake

@@ -1,4 +1,2 @@
-SET(CMAKE_SHARED_LIBRARY_CREATE_CXX_FLAGS "-G -Wl,-brtl,-bnoipath")       # -shared
-SET(CMAKE_SHARED_LIBRARY_LINK_CXX_FLAGS "-Wl,-brtl,-bnoipath,-bexpall")  # +s, flag for exe link to use shared lib
-SET(CMAKE_SHARED_LIBRARY_CXX_FLAGS " ")
-SET(CMAKE_SHARED_MODULE_CXX_FLAGS  " ")
+include(Platform/AIX-XL)
+__aix_compiler_xl(CXX)

Modules/Platform/AIX-XL-Fortran.cmake

@@ -1,4 +1,2 @@
-SET(CMAKE_SHARED_LIBRARY_CREATE_Fortran_FLAGS "-G -Wl,-brtl,-bnoipath")  # -shared
-SET(CMAKE_SHARED_LIBRARY_LINK_Fortran_FLAGS "-Wl,-brtl,-bnoipath,-bexpall")  # +s, flag for exe link to use shared lib
-SET(CMAKE_SHARED_LIBRARY_Fortran_FLAGS " ")
-SET(CMAKE_SHARED_MODULE_Fortran_FLAGS  " ")
+include(Platform/AIX-XL)
+__aix_compiler_xl(Fortran)

Modules/Platform/AIX-XL.cmake

@@ -0,0 +1,26 @@
+
+#=============================================================================
+# Copyright 2002-2011 Kitware, Inc.
+#
+# Distributed under the OSI-approved BSD License (the "License");
+# see accompanying file Copyright.txt for details.
+#
+# This software is distributed WITHOUT ANY WARRANTY; without even the
+# implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+# See the License for more information.
+#=============================================================================
+# (To distribute this file outside of CMake, substitute the full
+#  License text for the above reference.)
+
+# This module is shared by multiple languages; use include blocker.
+if(__AIX_COMPILER_XL)
+  return()
+endif()
+set(__AIX_COMPILER_XL 1)
+
+macro(__aix_compiler_xl lang)
+  set(CMAKE_SHARED_LIBRARY_CREATE_${lang}_FLAGS "-G -Wl,-brtl,-bnoipath")  # -shared
+  set(CMAKE_SHARED_LIBRARY_LINK_${lang}_FLAGS "-Wl,-brtl,-bnoipath,-bexpall")  # +s, flag for exe link to use shared lib
+  set(CMAKE_SHARED_LIBRARY_${lang}_FLAGS " ")
+  set(CMAKE_SHARED_MODULE_${lang}_FLAGS  " ")
+endmacro()