gcc: move patch folder to correct version, delete old csky patch

toolchain/gcc/patches/gcc-6-branch-csky/gcc7.patch

@@ -1,12 +0,0 @@
-diff -Nur gcc-gcc-6-branch-csky.orig/gcc/ubsan.c gcc-gcc-6-branch-csky/gcc/ubsan.c
---- gcc-gcc-6-branch-csky.orig/gcc/ubsan.c	2018-03-10 14:10:55.000000000 +0100
-+++ gcc-gcc-6-branch-csky/gcc/ubsan.c	2018-03-10 21:16:06.358370414 +0100
-@@ -1471,7 +1471,7 @@
- 
-   expanded_location xloc = expand_location (loc);
-   if (xloc.file == NULL || strncmp (xloc.file, "\1", 2) == 0
--      || xloc.file == '\0' || xloc.file[0] == '\xff'
-+      || xloc.file[0] == '\0' || xloc.file[0] == '\xff'
-       || xloc.file[1] == '\xff')
-     return false;
-