VS6: Rename some variables to correspond to config values.

This simplifies population of the compile flags.
Merge topic 'target-COMPILE_OPTIONS' into next

59c6db2 VS6: Rename some variables to correspond to config values.
VS6: Rename some variables to correspond to config values.

This simplifies population of the compile flags.
Add cmLocalGenerator::GetCompileOptions.

Currently it only adds the contents of the COMPILE_FLAGS target
property, but it can be extended to handle a new COMPILE_OPTIONS
generator expression enabled property.
Add <LANG>_COMPILER_ID generator expressions.

These expressions evaluate to the id of the compiler used to build
the target, or can be used to test if the compiler id matches a
specified value.
cmTarget: Rename struct to be more re-usable.

The same struct can be used to represent COMPILE_OPTIONS content.
cmTarget: Rename LinkInterfaceIncludeDirectoriesEntries

This can be used for COMPILE_OPTIONS too.
Add COMPILE_OPTIONS target property.

This method reads generator expressions from the COMPILE_OPTIONS
target property, as well as INTERFACE_COMPILE_OPTIONS from linked
dependents.
Add target_compile_options command.

This command populates the COMPILE_OPTIONS target property.
Merge topic 'target-COMPILE_OPTIONS' into next

710ef20 Add target_compile_options command.
6779749 Add COMPILE_OPTIONS target property.
71a1b62 cmTarget: Rename LinkInterfaceIncludeDirectoriesEntries
dd14aea cmTarget: Rename struct to be more re-usable.
5822d33 Add <LANG>_COMPILER_ID generator expressions.
82d063c Add cmLocalGenerator::GetCompileOptions.
cf1a667 VS6: Rename some variables to correspond to config values.