Building the POSIX binding using mmc --make by default and just have mmake
forward its work to that. Using mmc --make means things like library grade
exclusions will work properly.
Exclude non-C grades from the grade set in which to install the POSIX binding.
Shift a POSIX binding sample into the samples subdirectory.
extras/posix/Makefile:
extras/posix/Mercury.options:
Build the POSIX binding using mmc --make.
extras/posix/Mmakefile:
Redirect mmake to use the normal Makefile.
extras/posix/hello.m:
Shift this file into the samples subdirectory.
extras/samples/Makefile:
Set up things to build the samples against a libposix in the
parent directory.
extras/samples/Mmakefile:
Delete this file.
