libc/glibc: add multilib-cacpable backend

For mutlilib, the C library must be built once for each variants.
Special care must be taken to put the resulting libraries in
the proper places.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

libc/glibc: fix code formatting

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

libc/glib: pass installation subdir to backend

When building a multilib variant, install in a separate directory, to
avoid clutering the default or any other variant.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

libc/glibc: set the endian option according to extra CFLAGS

When building a multilib, some extra CFLAGS can override the
default config option. This is the case for the endianness
selection.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

libc/glibc: set the float option according to extra CFLAGS

When building a multilib, some extra CFLAGS can override the
default config option. This is the case for the floating point
selection.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

libc/glibc: add extra CFLAGS when building the C library

When building multilib, we need extra CFLAGS that tell the compiler
to use non-default settings (eg. big/little endian, hard/soft float,
-march/cpu/tune flags, and so on...).

We have to pass these flags to the build.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

libc/glibc: no default mode for backend

The caller SHALL explicitly ask for a nmode, and not rely on a default mode.
That's what actually happens, so we can get rid of the default.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

cc/gcc: print supported multilibs

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

cc/gcc: build multilib

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

binutils/binutils: build multilib

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>