gcc: add support for SOURCE_DATE_EPOCH environment

+ Create symlinks from gcc/patches/libcpp-source_date_epoch.patch to cross-*/files/
+ Make all the _apply_patch() functions the same

common/hooks/post-install/07-cleanup-timestamp-macros.sh

@@ -1,27 +0,0 @@
-# Remove leaked CFLAGS and CXXFLAGS parts which were defined
-# by common/hooks/pre-configure/03-timestamp-macros.sh
-# from shell scripts, perl scripts, package config files etc.
-
-hook() {
-	local f mimetype
-	local strip=" -Wno-builtin-macro-redefined -include${XBPS_BUILDDIR}/\.xbps-.*/timestamp-macros\.h"
-
-	[ -n "$XBPS_USE_BUILD_MTIME" ] && return 0
-	[ -z "$SOURCE_DATE_EPOCH" ] && return 0
-
-	# Clean up shell scripts, perl files, pkgconfig files etc.
-	for f in $(grep -r -l -e "$strip" "$PKGDESTDIR" ); do
-		mimetype=$(file --mime-type "$f" | awk '{ print $2 }')
-		if [ "$mimetype" == "text/plain" -o \
-		     "$mimetype" == "text/x-makefile" -o \
-		     "$mimetype" == "text/x-shellscript" -o \
-		     "$mimetype" == "application/xml" ]; then
-			sed -i "$f" -e "s;$strip;;"
-			msg_warn "Cleaned up ${f#${PKGDESTDIR}} ...\n"
-		else
-			# Unhandled mime-type file contains the $strip string
-			# E.g. binaries containing the build environment as a string
-			msg_warn "Can't clean ${f#${PKGDESTDIR}} (mime-type: $mimetype) ...\n"
-		fi
-	done
-}