MDEV-18506 MSI can't be built if MFC package is not installed with Visual Studio

candle.exe's preprocessor flags (-dHaveUpgradeWizard=0 -DHaveInnodb=1)
were not passed correctly to EXECUTE_PROCESS

Fix is to make a list out of the EXTRA_WIX_PREPROCESSOR_FLAGS string,
and use the preprocessor flags list in EXECUTE_PROCESS.

win/packaging/create_msi.cmake.in

@@ -401,9 +401,10 @@ IF("$ENV{EXTRA_LIGHT_ARGS}")
 ENDIF()
 
 FILE(REMOVE mysql_server.wixobj extra.wixobj)
+STRING(REPLACE " " ";" EXTRA_WIX_PREPROCESSOR_FLAGS_LIST ${EXTRA_WIX_PREPROCESSOR_FLAGS})
 EXECUTE_PROCESS(
  COMMAND ${CANDLE_EXECUTABLE} 
- ${EXTRA_WIX_PREPROCESSOR_FLAGS} 
+ ${EXTRA_WIX_PREPROCESSOR_FLAGS_LIST}
  ${CANDLE_ARCH} 
  -ext WixUtilExtension 
  -ext WixFirewallExtension   
@@ -413,7 +414,7 @@ EXECUTE_PROCESS(
 
 EXECUTE_PROCESS(
  COMMAND ${CANDLE_EXECUTABLE} ${CANDLE_ARCH}
- ${EXTRA_WIX_PREPROCESSOR_FLAGS} 
+ ${EXTRA_WIX_PREPROCESSOR_FLAGS_LIST}
  -ext WixUtilExtension 
  -ext WixFirewallExtension  
  ${CMAKE_CURRENT_BINARY_DIR}/extra.wxs