Merge pull request #9 from fortanix/jb/unsafecell-niche-fix

Actually fix RWLock representation for UnsafeCell niche fix

Author: mzohreva

libunwind/src/UnwindRustSgx.h

@@ -22,9 +22,9 @@
 
 // We have to use RWLock from rust repo, it is defined in:
 // src/libstd/sys/sgx/rwlock.rs.
-// rwlock.rs has compile time check to ensure sizeof(RWLock) = 128.
+// rwlock.rs has compile time check to ensure sizeof(RWLock) = 144.
 typedef struct {
-    unsigned char opaque[128];
+    unsigned char opaque[144];
 } RWLock;
 
 // The below is obtained by printing initialized bytes

libunwind/src/UnwindRustSgxSnprintf.c

@@ -10,7 +10,9 @@
 #pragma GCC diagnostic ignored "-Wfloat-conversion"
 #pragma GCC diagnostic ignored "-Wsign-conversion"
 #pragma GCC diagnostic ignored "-Wstrict-overflow"
+#if __GNUC__ >= 7
 #pragma GCC diagnostic ignored "-Wimplicit-fallthrough"
+#endif
 
 /**************************************************************
  * Original: