coordlist_ops: adjust memcpy call for macro

[iamleot]

In some SSP implementations - like NetBSD ssp(3) - memcpy(3) can be a macro and the build will fail because the macro will see 8 arguments instead of 3.

Actual build error, included for convenience:

[ 69%] Building C object CMakeFiles/gromit-mpx.dir/src/coordlist_ops.c.o
.../pkgsrc/wip/gromit-mpx/work/gromit-mpx-1.7.0/src/coordlist_ops.c: In function 'unity2D':
.../pkgsrc/wip/gromit-mpx/work/gromit-mpx-1.7.0/src/coordlist_ops.c:273:78: error: macro "memcpy" passed 8 arguments, but takes just 3
  273 |     memcpy(m->m, (gfloat[6]){1.0, 0.0, 0.0, 0.0, 1.0, 0.0}, sizeof(gfloat[6]));
      |                                                                              ^
In file included from /usr/include/string.h:128,
                 from .../pkgsrc/wip/gromit-mpx/work/gromit-mpx-1.7.0/src/coordlist_ops.c:26:
/usr/include/ssp/string.h:95: note: macro "memcpy" defined here
   95 | #define memcpy(dst, src, len) __ssp_bos_check3(memcpy, dst, src, len)
      |
.../pkgsrc/wip/gromit-mpx/work/gromit-mpx-1.7.0/src/coordlist_ops.c:273:5: warning: statement with no effect [-Wunused-value]
  273 |     memcpy(m->m, (gfloat[6]){1.0, 0.0, 0.0, 0.0, 1.0, 0.0}, sizeof(gfloat[6]));
      |     ^~~~~~

I have noticed it while packaging gromit-mpx in pkgsrc on NetBSD.

[bk138]

Well-crafted PR, thanks!