distro: gcc: Don't add a RUNPATH to GCC when using `-static-libgcc'.

* distro/packages/base.scm (gcc-4.7)[LIB_SPEC]: Add a `-rpath' to GCC
  only when !static and !static-libgcc.

distro/packages/base.scm

@@ -400,8 +400,11 @@ (define-public gcc-4.7
                  (substitute* (find-files "gcc/config"
                                           "^(gnu-user(64)?|linux-elf)\\.h$")
                    (("#define LIB_SPEC (.*)$" _ suffix)
-                    (format #f "#define LIB_SPEC \"-L~a/lib -rpath=~a/lib \
--rpath=~a/lib64 -rpath=~a/lib \" ~a~%"
+                    ;; Note that with this "lib" spec, we may still add a
+                    ;; RUNPATH to GCC even when `libgcc_s' is not NEEDED.
+                    ;; There's not much that can be done to avoid it, though.
+                    (format #f "#define LIB_SPEC \"-L~a/lib %{!static:-rpath=~a/lib \
+%{!static-libgcc:-rpath=~a/lib64 -rpath=~a/lib}} \" ~a~%"
                             libc libc out out suffix))
                    (("#define STARTFILE_SPEC.*$" line)
                     (format #f "#define STANDARD_STARTFILE_PREFIX_1 \"~a/lib\"