#2141 Commit [b83c88] breaks windows build (time.c)

[Tatsuro MATSUOKA]

Commit [b83c88] break windows build (time.c).

gcc -c -DDEFAULTTERM=\"wxt\" -m32 -O2 -pipe -DUNICODE -D_UNICODE -Wno-unused-function -DGNUPLOT_PS_DIR=\"share/PostScript\"  -I. -I../../src -I../../term/ -DHAVE_CONFIG_H -D__USE_MINGW_ANSI_STDIO=1 -DGNUPLOT_SHARE_DIR=\"share\" -DDEVELOPMENT_VERSION -DUSE_MOUSE=1 -DWIN_IPC -I/c/Program\ Files\ \(x86\)/HTML\ Help\ Workshop/include -DHAVE_LIBGD -DHAVE_LIBPNG -DHAVE_LIBGD -DHAVE_GD_H -DHAVE_GD_GIF -DGIF_ANIMATION -DHAVE_GD_PNG -IC:/msys64/mingw32/include/ -DHAVE_GD_JPEG -DHAVE_GD_TTF -DHAVE_CAIROPDF -DWXWIDGETS -DQTTERM -DQT_NO_OPENGL -DHAVE_LUA -DHAVE_LIBCACA -DHAVE_ICONV -DHAVE_LIBCERF -DNEED_CEXP -DREADLINE -DHAVE_D2D11 -DPIPES -MMD -MT 'time.o' -MF time.d -o time.o ../../src/time.c
../../src/time.c: In function 'gstrptime':
../../src/time.c:107:9: error: 'struct tm' has no member named 'tm_gmtoff'; did you mean 'tm_mon'?
     tm->tm_gmtoff = DEFAULT_TZ;
         ^~~~~~~~~
         tm_mon
../../src/time.c:308:7: error: 'struct tm' has no member named 'tm_gmtoff'; did you mean 'tm_mon'?
   tm->tm_gmtoff = 3600*off_h + 60*off_m;
       ^~~~~~~~~
       tm_mon
../../src/time.c:309:7: error: 'struct tm' has no member named 'tm_gmtoff'; did you mean 'tm_mon'?
   tm->tm_gmtoff *= neg;
       ^~~~~~~~~
       tm_mon
../../src/time.c: In function 'gtimegm':
../../src/time.c:777:17: error: 'struct tm' has no member named 'tm_gmtoff'; did you mean 'tm_mon'?
     dsec -= tm->tm_gmtoff;
                 ^~~~~~~~~
                 tm_mon
../../src/time.c: In function 'ggmtime':
../../src/time.c:802:9: error: 'struct tm' has no member named 'tm_gmtoff'; did you mean 'tm_mon'?
     tm->tm_gmtoff = DEFAULT_TZ;
         ^~~~~~~~~
         tm_mon
make: *** [Makefile:609: time.o] Error 1

On cygwin and Ubuntu 18.04 (on WSL), errors do not appear.

[Ethan Merritt]

Sorry.
I added an autoconf check, which Windows will not use

[Tatsuro MATSUOKA]

I have confirmed the fix. Thanks!