Correctly define malloc_usable_size

Get correct abort() function definition for Solaris.

diff --git a/memory/mozalloc/mozalloc.cpp b/memory/mozalloc/mozalloc.cpp
--- a/memory/mozalloc/mozalloc.cpp
+++ b/memory/mozalloc/mozalloc.cpp
@@ -197,6 +197,8 @@
 #endif // if defined(HAVE_VALLOC)
 
 #ifndef MOZ_STATIC_RUNTIME
+extern "C" size_t malloc_usable_size(const void *ptr);
+
 size_t
 moz_malloc_usable_size(void *ptr)
 {
diff --git a/memory/mozalloc/mozalloc_abort.cpp b/memory/mozalloc/mozalloc_abort.cpp
--- a/memory/mozalloc/mozalloc_abort.cpp
+++ b/memory/mozalloc/mozalloc_abort.cpp
@@ -63,7 +63,11 @@
 //
 // That segmentation fault will be interpreted as another bug by ASan and as a
 // result, ASan will just exit(1) instead of aborting.
+#if defined(SOLARIS)
+void std::abort(void)
+#else
 void abort(void)
+#endif
 {
 #ifdef MOZ_WIDGET_ANDROID
     char msg[64] = {};