Add gcc4 and gcc4-armhf packages (!216)

Successfully tested both the gcc4 compiler on x86_64 with a simple
program (fbdebug) and the gcc4-armhf cross-compiler to build a very old
u-boot port for Galaxy Nexus (a MR will follow soon) which failed to
boot with either newer version (6 and 8).

[skip ci]: already went through

main/gcc4/15_all_libgfortran-Werror.patch

@@ -0,0 +1,17 @@
+libgfortran does not respect --disable-werror
+
+https://bugs.gentoo.org/433435
+http://gcc.gnu.org/PR54724
+
+
+--- a/libgfortran/configure
++++ b/libgfortran/configure
+@@ -5764,7 +5764,7 @@ fi
+ 
+ # Add -Wall -fno-repack-arrays -fno-underscoring if we are using GCC.
+ if test "x$GCC" = "xyes"; then
+-  AM_FCFLAGS="-I . -Wall -Werror -fimplicit-none -fno-repack-arrays -fno-underscoring"
++  AM_FCFLAGS="-I . -Wall -fimplicit-none -fno-repack-arrays -fno-underscoring"
+   ## We like to use C99 routines when available.  This makes sure that
+   ## __STDC_VERSION__ is set such that libc includes make them available.
+   AM_CFLAGS="-std=gnu99 -Wall -Wstrict-prototypes -Wmissing-prototypes -Wold-style-definition -Wextra -Wwrite-strings"