move libgcc.h to include/linux

Introducing a new include/lib directory just for this file totally
messes up tab completion for include/linux, which is highly annoying.

Move it to include/linux where we have headers for all kinds of other
lib/ code as well.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Palmer Dabbelt <palmer@sifive.com>
diff --git a/lib/muldi3.c b/lib/muldi3.c
index 8893854..54c8b31 100644
--- a/lib/muldi3.c
+++ b/lib/muldi3.c
@@ -15,7 +15,7 @@
  */
 
 #include <linux/export.h>
-#include <lib/libgcc.h>
+#include <linux/libgcc.h>
 
 #define W_TYPE_SIZE 32