bootstrap: Do not save compiler flags to mk.conf.

We already set them explicitly in pkgbuild and besides avoiding
duplicates this also allows us to change them without having to rebuild
bootstrap.

bootstrap/bootstrap

@@ -1307,6 +1307,7 @@ if test -n "$XARGS"; then
 	echo "TOOLS_PLATFORM.xargs?=		$XARGS" >> ${TARGET_MKCONF}
 	echo "TOOLS_PLATFORM.xargs?=		$XARGS" >> ${BOOTSTRAP_MKCONF}
 fi
+if false; then
 if test -n "$CFLAGS"; then
 	echo "CFLAGS+=		$CFLAGS" >> ${TARGET_MKCONF}
 	echo "DBG=			# prevent DBG from adding default optimizer flags" >> ${TARGET_MKCONF}
@@ -1321,6 +1322,7 @@ fi
 if test -n "$LIBS"; then
 	echo "LIBS+=		$LIBS" >> ${TARGET_MKCONF}
 fi
+fi
 
 # opsys specific fiddling
 opsys_finish