gcc: allow stripping gcc libraries

When cross compiling to the same kernel / arch combination, it is safe
to use strip of libraries. This happens when cross-compiling musl
programs. dontStrip is now set in each gcc compiler instead of in
gcc/builder.sh.

Fixes #75476

pkgs/development/compilers/gcc/builder.sh

@@ -147,9 +147,9 @@ if test "$noSysDirs" = "1"; then
     fi
 fi
 
-if test -n "${targetConfig-}"; then
-    # The host strip will destroy some important details of the objects
-    dontStrip=1
+if [ -n "${targetConfig-}" ]; then
+    # if stripping gcc, include target directory too
+    stripDebugList="${stripDebugList-lib lib32 lib64 libexec bin sbin} $targetConfig"
 fi
 
 eval "$oldOpts"