glibc: fix fortran header file conflict for arm

glibc: fix fortran header file conflict for arm

There is a file conflict for arm when multilib enabled:

| Error: Transaction test error:
|   file /usr/include/finclude/math-vector-fortran.h conflicts between attempted installs of
    lib32-libc6-dev-2.39+git0+312e159626-r0.armv7at2hf_neon and libc6-dev-2.39+git0+312e159626-r0.cortexa72

Install math-vector-fortran.h to the gfortran default search directory
which is arch specific to avoid the conflict.

Signed-off-by: Kai Kang <kai.kang@windriver.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>