aarch64: Fix noexecstack note in libgcc

lse.S did not have GNU stack note, this may cause missing
PT_GNU_STACK in binaries on Linux and FreeBSD.

2020-07-09  Szabolcs Nagy  <szabolcs.nagy@arm.com>

libgcc/ChangeLog:

	* config/aarch64/lse.S: Add stack note.

(cherry picked from commit e73ec755489afc9fcc75dfac6f06ac73e243e72a)

libgcc/config/aarch64/lse.S

@@ -274,3 +274,7 @@ STARTFN	NAME(LDNM)
 
 ENDFN	NAME(LDNM)
 #endif
+
+#if defined(__linux__) || defined(__FreeBSD__)
+.section .note.GNU-stack, "", %progbits
+#endif