Adaptations for building with bionic libc under termux

When using glib as a meson subproject and attempting builds under termux, without a proot based chroot for a linux distro, the glib stages of the build fails - mostly in tests due to symbol shadowing|conflicts, I guess this possibly due to the toolchain having global declarations of some of libc.

glib-gegl-termux-build-output.txt Search for "errors generated" and "error generated" for the specific errors being worked around.

Individual patches for the fixes/workarounds: 0001-gio-define-hasmntopt-ourselves-under-bionic-libc.patch 0002-gio-tests-avoid-shadowing-of-libc-names-under-bionic.patch 0003-glib-tests-evade-bionic-libc-polyfills-for-getpwuid.patch