[tlbuild] Failure to build mpfr from TL: 'gmp.h' file not found

[Mojca Miklavec]

Hi,

I installed a new VM with OpenBSD 6.7 and tried to install just the
bare minimum of packages.

Apparently the build now fails when configuring mpfr.

configure:6707: cc -c -g -O2 --float-store
-I/path/to/texlive/source/Work/libs/gmp/include conftest.c >&5
conftest.c:66:10: fatal error: 'gmp.h' file not found
#include <gmp.h>

The file gmp.h is present under
    /path/to/texlive/source/Work/libs/gmp/gmp.h
but not under gmp/include/gmp.h as the include path suggests.

I suspect that the problem might generally be hidden since it's easy
to find this header elsewhere on the system, but I don't know for
sure.

The configure line likely comes from TeX Live's own mpfr/configure.ac:
    AC_CHECK_HEADER([gmp.h], [], [AC_MSG_ERROR[gmp.h not found]])
maybe the command
    KPSE_ADD_FLAGS([gmp])
doesn't take all corner cases into account and adds the "include/"
folder to the include path which happens to be missing in the build
tree for gmp.

Mojca