MinGW: getch.c does not build, no option to work around via Makefile

[GitMensch]

Sadly the current release does not build with "old MinGW" any more (last tested with 4.4.0, which worked out of the box):

cd wincon && make INFOEX=N CHTYPE_64=Y DEBUG=Y DLL=Y DLLNAME=libpdcurses LIBNAME=libpdcurses.dll"
gcc -c -Wall -Wextra -pedantic -g -DPDCDEBUG -I.. -DPDC_DLL_BUILD ../pdcurses/addch.c
gcc -c -Wall -Wextra -pedantic -g -DPDCDEBUG -I.. -DPDC_DLL_BUILD ../pdcurses/addchstr.c
gcc -c -Wall -Wextra -pedantic -g -DPDCDEBUG -I.. -DPDC_DLL_BUILD ../pdcurses/addstr.c
gcc -c -Wall -Wextra -pedantic -g -DPDCDEBUG -I.. -DPDC_DLL_BUILD ../pdcurses/attr.c
gcc -c -Wall -Wextra -pedantic -g -DPDCDEBUG -I.. -DPDC_DLL_BUILD ../pdcurses/beep.c
gcc -c -Wall -Wextra -pedantic -g -DPDCDEBUG -I.. -DPDC_DLL_BUILD ../pdcurses/bkgd.c
gcc -c -Wall -Wextra -pedantic -g -DPDCDEBUG -I.. -DPDC_DLL_BUILD ../pdcurses/border.c
gcc -c -Wall -Wextra -pedantic -g -DPDCDEBUG -I.. -DPDC_DLL_BUILD ../pdcurses/clear.c
gcc -c -Wall -Wextra -pedantic -g -DPDCDEBUG -I.. -DPDC_DLL_BUILD ../pdcurses/color.c
gcc -c -Wall -Wextra -pedantic -g -DPDCDEBUG -I.. -DPDC_DLL_BUILD ../pdcurses/debug.c
gcc -c -Wall -Wextra -pedantic -g -DPDCDEBUG -I.. -DPDC_DLL_BUILD ../pdcurses/delch.c
gcc -c -Wall -Wextra -pedantic -g -DPDCDEBUG -I.. -DPDC_DLL_BUILD ../pdcurses/deleteln.c
gcc -c -Wall -Wextra -pedantic -g -DPDCDEBUG -I.. -DPDC_DLL_BUILD ../pdcurses/getch.c
../pdcurses/getch.c: In function 'PDC_millisecs':
../pdcurses/getch.c:439:5: warning: implicit declaration of function 'clock_gettime' [-Wimplicit-function-declaration]
     clock_gettime( CLOCK_REALTIME, &t);
     ^
../pdcurses/getch.c:439:20: error: 'CLOCK_REALTIME' undeclared (first use in this function)
     clock_gettime( CLOCK_REALTIME, &t);
                    ^
../pdcurses/getch.c:439:20: note: each undeclared identifier is reported only once for each function it appears in
make: *** [getch.o] Error 1
Command exited with code 2

and the only workaround is to either adjust the makefile (because PDCCFLAGS only applies to osdir, but not srcdir, otherwise make PDCCFLAGS=-DHAVE_GETTIMEOFDAY would have worked) or getch.c.

Originally posted by @GitMensch in #344 (comment)

[GitMensch]

@Bill-Gray While this is now solved via code, you may want to check the Makefiles - how should a user add to CFLAGS "from the outside" (for gcc in wincon + wingui I found no "direct" option)?

[Bill-Gray]

Um. I don't know if there's a "standard" method for doing this? I'd think there would be, but can't say I've ever encountered it...

I just tried adding the line

CFLAGS += $(ADDED_CFLAGS)

and running make (usual flags) ADDED_CFLAGS=-DGARBAGE, and GARBAGE was suitably defined. Such a technique could be used for all makefiles, I think. It works, but I'd like to verify that we're not re-inventing a wheel here before committing changes.

(As a side issue, it'd still be nice to make the "correct" distinction between CPPFLAGS, used for the C preprocessor, and "regular" CFLAGS, in a variety of our Makefiles. Not a big deal, but it was mentioned recently, and it's hard for me to un-see it now.)

[GitMensch]

The documentation for autotools effectively says:
CFLAGS, LIBS, LDFLAGS, CPPFLAGS, ... all "belong to the user":

• one should not override them
• all "project owned" vars have a prefix (like PDC_)
• the "normal" ones are used in the makefiles (either side-by side with the "project owned" ones or by or adding them to those)

I think that's a good rule.

[GitMensch]

Rechecked: clock_gettime was added in 2017 to MinGW: https://sourceforge.net/p/mingw/bugs/2349; as noted in its addition:

POSIX.1b-1993 introduced the optional POSIX clocks API; it
was subsequently moved to "base", as of POSIX.1-2008, to the
extent required to support the CLOCK_REALTIME feature, with
the remainder of its features remaining optional. We choose
to provide a subset, supporting CLOCK_MONOTONIC in addition
to the aforementioned CLOCK_REALTIME feature.

Note: our check with 1993 was wrong, but even "the correct one 2008" would have gone wrong because that is specified by old MinGW as default - without the then mandatory posix timers.

So getch.c's current check seems wrong, additional to the posix version we should check _POSIX_TIMERS to be defined and not -1.
I've also found _XOPEN_REALTIME but it seems that is broader and if defined also the other macro would be defined.

Reopen for another take.