WL#5161: Implement Mats' suggestion of moving OS specific CMake code to OS specific files, instead of

polluting code with IF(CMAKE_SYSTEM_NAME MATCHES...), first on Windows.

cmake/libutils.cmake:
  Fix the case in MERGE_LIBRARIES, where  there is no dependency on OS libraries.
cmake/os/Windows.cmake:
  Move windows specific code to cmake/os/Windows.cmake
configure.cmake:
  Move some Windows code to cmake/os/Windows.cmake

CMakeLists.txt

@@ -61,6 +61,25 @@ ENDIF()
 
 PROJECT(MySQL)
 
+# Include the platform-specific file. To allow exceptions, this code
+# looks for files in order of how specific they are. If there is, for
+# example, a generic Linux.cmake and a version-specific
+# Linux-2.6.28-11-generic, it will pick Linux-2.6.28-11-generic and
+# include it. It is then up to the file writer to include the generic
+# version if necessary.
+FOREACH(_base
+    ${CMAKE_SYSTEM_NAME}-${CMAKE_SYSTEM_VERSION}-${CMAKE_SYSTEM_PROCESSOR}
+    ${CMAKE_SYSTEM_NAME}-${CMAKE_SYSTEM_VERSION}
+    ${CMAKE_SYSTEM_NAME})
+  SET(_file ${CMAKE_SOURCE_DIR}/cmake/os/${_base}.cmake)
+  IF(EXISTS ${_file})
+    INCLUDE(${_file})
+    BREAK()
+  ENDIF()
+ENDFOREACH()
+
+
+
 # Following autotools tradition, add preprocessor definitions
 # specified in environment variable CPPFLAGS
 IF(DEFINED ENV{CPPFLAGS})
@@ -71,12 +90,6 @@ IF(CYGWIN)
   SET(WIN32 0)
 ENDIF()
 
-IF(WIN32)
-  SET(IF_WIN 0)
-ELSE()
-  SET(IF_WIN 1)
-ENDIF()
-
 # Add macros
 INCLUDE(character_sets)
 INCLUDE(zlib)
@@ -163,8 +176,6 @@ IF(WITH_DEBUG OR WITH_DEBUG_FULL AND NOT WIN32)
 ENDIF()
 
 
-
-
 # Set commonly used variables
 IF(WIN32)
   SET(DEFAULT_MYSQL_HOME "C:/Program Files/MySQL/MySQL Server ${MYSQL_BASE_VERSION}" )
@@ -184,12 +195,6 @@ IF(SYSCONFDIR)
 ENDIF()
 
 
-# Optionally read user configuration, generated by configure.js.
-# This is left for backward compatibility reasons only.
-IF(WIN32)
- INCLUDE(win/configure.data OPTIONAL)
-ENDIF()
-
 # Run platform tests
 INCLUDE(configure.cmake)