mk: Fix REQUIRES generation for non-standard paths.

The GCC packages were incorrectly generating REQUIRES for GCC runtime
libraries found under /usr/lib/amd64, because the REQUIRES handling did
not account for the paths that GCC uses to store its runtime libraries.

Instead of only looking in ${DESTDIR}${PREFIX}/lib, look under
${DESTDIR} first for all RPATH entries used by the target object.

GCC now correctly does not list any REQUIRES for its own libraries.

mk/pkgformat/pkg/metadata.mk

@@ -71,11 +71,20 @@ ${_BUILD_INFO_FILE}: ${_PLIST_NOKEYWORDS}
 					dsolibs = dsolibs (dsolibs ? ":" : "") $$NF;				\
 				}										\
 				/RPATH/ {									\
-					nrpath = split($$NF ":${DESTDIR}${PREFIX}/lib${LIBARCHSUFFIX}:${SYSTEM_DEFAULT_RPATH}", rpath, ":"); \
+					nrpath = split($$NF ":${SYSTEM_DEFAULT_RPATH}", rpath, ":");		\
 					nlibs = split(dsolibs, libs, ":");					\
 					for (l = 1; l <= nlibs; l++) {						\
 						for (r = 1; r <= nrpath; r++) {					\
 							sub(/\/$$/, "", rpath[r]);				\
+							sub(/\/\.$$/, "", rpath[r]);				\
+							libfile = "${DESTDIR}" rpath[r] "/" libs[l];		\
+							if (!(libfile in libcache)) {				\
+								libcache[libfile] = system("test -f " libfile); \
+							}							\
+							if (libcache[libfile] == 0) {				\
+								print libfile;					\
+								break;						\
+							}							\
 							libfile = rpath[r] "/" libs[l];				\
 							if (!(libfile in libcache)) {				\
 								libcache[libfile] = system("test -f " libfile); \