Ignore weak symbols in check-symbols.sh

Some clang versions leave a std::round(float) weak symbol around...
diff --git a/src/check-symbols.sh b/src/check-symbols.sh
index d4eca50..6e9382b 100755
--- a/src/check-symbols.sh
+++ b/src/check-symbols.sh
@@ -26,7 +26,7 @@
 		symprefix=
 		if test $suffix = dylib; then symprefix=_; fi
 
-		EXPORTED_SYMBOLS="`nm "$so" | grep ' [BCDGINRSTVW] .' | grep -v " $symprefix\\($IGNORED_SYMBOLS\\>\\)" | cut -d' ' -f3 | c++filt`"
+		EXPORTED_SYMBOLS="`nm "$so" | grep ' [BCDGINRSTV] .' | grep -v " $symprefix\\($IGNORED_SYMBOLS\\>\\)" | cut -d' ' -f3 | c++filt`"
 
 		prefix=$symprefix`basename "$so" | sed 's/libharfbuzz/hb/; s/-/_/g; s/[.].*//'`