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/gcc4/10_all_default-fortify-source.patch

@@ -0,0 +1,31 @@
+Enable -D_FORTIFY_SOURCE=2 by default.
+
+Original patch from:
+http://sources.gentoo.org/cgi-bin/viewvc.cgi/gentoo/src/patchsets/gcc/4.9.2/gentoo/10_all_default-fortify-source.patch
+
+--- a/gcc/c-family/c-cppbuiltin.c
++++ b/gcc/c-family/c-cppbuiltin.c
+@@ -951,6 +951,9 @@ c_cpp_builtins (cpp_reader *pfile)
+   builtin_define_with_value ("__REGISTER_PREFIX__", REGISTER_PREFIX, 0);
+   builtin_define_with_value ("__USER_LABEL_PREFIX__", user_label_prefix, 0);
+ 
++  /* Fortify Source enabled by default w/optimization.  */
++  cpp_define (pfile, "_FORTIFY_SOURCE=((defined __OPTIMIZE__ && __OPTIMIZE__ > 0) ? 2 : 0)");
++
+   /* Misc.  */
+   if (flag_gnu89_inline)
+     cpp_define (pfile, "__GNUC_GNU_INLINE__");
+--- a/gcc/doc/gcc.info
++++ b/gcc/doc/gcc.info
+@@ -6255,6 +6255,11 @@ find out the exact set of optimizations that are enabled at each level.
+      Please note the warning under '-fgcse' about invoking '-O2' on
+      programs that use computed gotos.
+ 
++     NOTE: In Alpine Linux, `-D_FORTIFY_SOURCE=2' is set by default, and is
++     activated when `-Os' or `-O1' or higher is used.  This enables additional
++     compile-time and run-time checks for several libc functions.  To disable,
++     specify either `-U_FORTIFY_SOURCE' or `-D_FORTIFY_SOURCE=0'.
++
+ '-O3'
+      Optimize yet more.  '-O3' turns on all optimizations specified by
+      '-O2' and also turns on the '-finline-functions',