Issue #457 - Silence SQLite compiler warning

Our use of SQLite explicitly avoids using MSVC's _msize which the lib would
notrmally use. This was set up this way in BZ bug 719579 for legitimate reasons
(because _msize would end up using the system symbol, which would crash trying
to get the size information from jemalloc allocations). Since we build the
SQLite lib separately there is no easy way to avoid this warning as it's not
directly linked against mozglue.dll which has the jemalloc functions it wants
for _msize when not using the system allocator. It is implicitly assuming the
function is an extern returning an int (with the call specifically  casting to
int) which is correct (well, correct _enough_, anyway) so the warning can
safely be ignored for our specific use as it all lines up at link time.

db/sqlite3/src/moz.build

@@ -65,9 +65,13 @@ if CONFIG['MOZ_DEBUG']:
 
 # Force using malloc_usable_size when building with jemalloc because _msize
 # causes assertions on Win64. See bug 719579.
+# This causes a known warning due to the way mozjemalloc is linked and the
+# malloc_usable_size function not being available at compile time on MSVC
+# so we suppress that particular warning (C4013)
 if CONFIG['OS_ARCH'] == 'WINNT' and CONFIG['MOZ_MEMORY']:
     DEFINES['HAVE_MALLOC_USABLE_SIZE'] = True
     DEFINES['SQLITE_WITHOUT_MSIZE'] = True
+    CFLAGS += ['-wd4013']
 
 # Omit unused functions to save some library footprint.
 DEFINES['SQLITE_OMIT_DEPRECATED'] = True