add nothrow attributes to jemalloc non-standard API declarations.

Summary: According to https://github.com/jemalloc/jemalloc/issues/237 and https://fburl.com/aeia78qk, `__attribute__((nothrow))` is added to jemalloc API functions to be in compatible with `stdlib.h`.

Reviewed By: yfeldblum

Differential Revision: D17679036

fbshipit-source-id: 525a076f19719d2406c0dce92ca814f5f5011497

folly/memory/detail/MallocImpl.h

@@ -23,18 +23,20 @@
 extern "C" {
 
 #if FOLLY_HAVE_WEAK_SYMBOLS
-void* mallocx(size_t, int) __attribute__((__weak__));
-void* rallocx(void*, size_t, int) __attribute__((__weak__));
-size_t xallocx(void*, size_t, size_t, int) __attribute__((__weak__));
-size_t sallocx(const void*, int) __attribute__((__weak__));
-void dallocx(void*, int) __attribute__((__weak__));
-void sdallocx(void*, size_t, int) __attribute__((__weak__));
-size_t nallocx(size_t, int) __attribute__((__weak__));
+void* mallocx(size_t, int) __attribute__((__nothrow__, __weak__));
+void* rallocx(void*, size_t, int) __attribute__((__nothrow__, __weak__));
+size_t xallocx(void*, size_t, size_t, int)
+    __attribute__((__nothrow__, __weak__));
+size_t sallocx(const void*, int) __attribute__((__nothrow__, __weak__));
+void dallocx(void*, int) __attribute__((__nothrow__, __weak__));
+void sdallocx(void*, size_t, int) __attribute__((__nothrow__, __weak__));
+size_t nallocx(size_t, int) __attribute__((__nothrow__, __weak__));
 int mallctl(const char*, void*, size_t*, void*, size_t)
-    __attribute__((__weak__));
-int mallctlnametomib(const char*, size_t*, size_t*) __attribute__((__weak__));
+    __attribute__((__nothrow__, __weak__));
+int mallctlnametomib(const char*, size_t*, size_t*)
+    __attribute__((__nothrow__, __weak__));
 int mallctlbymib(const size_t*, size_t, void*, size_t*, void*, size_t)
-    __attribute__((__weak__));
+    __attribute__((__nothrow__, __weak__));
 #else
 extern void* (*mallocx)(size_t, int);
 extern void* (*rallocx)(void*, size_t, int);