Expect cxx_variadic_templates to implement N2555.
N2555 is essentially a bugfix and predates most compiler releases which
aimed to experimentally support variadic templates.
Record the availability of this feature for GNU 4.8 on (UNIX AND
NOT APPLE) only. In the future, availability can be recorded for
earlier GNU, for other platforms and for other compilers. Initially
the affected configurations are as restricted as possible to allow
for easy testing while extending the features vector in only one
dimension.
The error message when using the set_property API directly is not
very good, but follow up commits will provide origin debugging of
the property and a target_compile_features command which will
provide a configure-time backtrace when possible.
Add a feature test using the compiler macros and the preprocessor to
determine available features.
Add a CMAKE_CXX_COMPILE_FEATURES variable which contains all features
known to the loaded compiler, and a CMAKE_CXX_KNOWN_FEATURES variable
containing all features known to CMake. Add language standard specific
variables for internal use to determine the standard-specific compile
flags to use.
This will be extended to other languages in the future. Follow-up
commits will add features which will be recorded by the feature test.
QT4_CREATE_MOC_COMMAND is given a moc_flags argument that contains the
COMPILE_DEFINITIONS and a potentially large list of include directories.
Since it is a macro, the ${moc_flags} reference is replaced with this
content and sent through cmMakefile::ExpandVariablesInString (EVIS).
Since commit v3.0.0-rc1~138^2 (Qt4: Use generator expression in
COMPILE_DEFINITIONS, 2014-01-13) the COMPILE_DEFINITIONS value contains
a '$' so the EVIS fast-path is no longer used. Instead the full
cmCommandArgumentParserHelper is now used on the large input, which is
very slow (since it was originally created for hand-written code).
Change QT4_CREATE_MOC_COMMAND to a function instead of a macro to avoid
passing large content through EVIS. This makes it significantly faster.
Stephen Kelly
Brad King
Robert Maynard