fix for MKC_CHECK_CUSTOM with non-empty MAKEOBJDIR
s/-KPIC/-xcode=pic32/ for SunStudio compiler
${MAKEFLAGS} is passed to recursive make invocations
MKC_CHECK_PROGS: PROG.<prog> is set even if full path was specified.
In addition existance and executability of the specified file is
always checked.
mkc_check_prog: option -i is documented in man page
long option --help was removed from all utilities
mkc.subprj.mk: new targets <subdir:T>, <trg-subdir:T> etc.
mkc_imp.subdir.mk was reimplemented using mkc_imp.subprj.mk; code clean-ups
TARGETS variable is sort-uniqued
TODO: a lot of new tasks
SUBDIR: code clean-ups
mkc_imp.intexts.mk fixes:
   - Targets "clean" and "cleandir" do not fail anymore if INTEXTS_REPLS
     contain unexpanded/empty variables
   - Target "all" works correctly if INFILES or INSCRIPTS contain
     files with directories.
TODO: one task done
additional files for tests/intexts_cleantrg regression test
Support for MKSSP=yes for IBM XL Compiler (not tested)
Support for MKSSP=yes for Intel C/C++ Compiler
.undef MKC_CHECK_VAR just like all other MKC_CHECK_*
More complex examples/hello_strlcpy
mk.configure.mk: fix for MKC_SOURCE_FUNCLIBS -> CLEANFILES.
Now all functions.o are added to CLEANFILES unconditionally.
minor code clean-ups