Fix CMAKE_<LANG>_COMPILER_TARGET with CMAKE_<LANG>_COMPILER_ARG1

In commit 2d9ec1da (Add compiler target compile options, 2013-05-19)
we taught cmLocalGenerator::ExpandRuleVariable to implement the
CMAKE_<LANG>_COMPILER_TARGET setting by adding the appropriate flag.
Fix the case when compilerArg1 is set to separate the target flag
from the preceding flags by a space.
Merge topic 'fix-COMPILER_TARGET-with-arg1' into next

dbfdf2f Fix CMAKE_<LANG>_COMPILER_TARGET with CMAKE_<LANG>_COMPILER_ARG1