Add JEMALLOC_CC_SILENCE_INIT().

Add JEMALLOC_CC_SILENCE_INIT(), which provides succinct syntax for
initializing a variable to avoid a spurious compiler warning.

include/jemalloc/internal/util.h

@@ -16,6 +16,17 @@
  */
 #define JEMALLOC_CONCAT(...) __VA_ARGS__
 
+/*
+ * Silence compiler warnings due to uninitialized values.  This is used
+ * wherever the compiler fails to recognize that the variable is never used
+ * uninitialized.
+ */
+#ifdef JEMALLOC_CC_SILENCE
+#  define JEMALLOC_CC_SILENCE_INIT(v) = v
+#else
+#  define JEMALLOC_CC_SILENCE_INIT(v)
+#endif
+
 /*
  * Define a custom assert() in order to reduce the chances of deadlock during
  * assertion failure.