clang does not support -mno-ieee-fp:
      https://llvm.org/bugs/show_bug.cgi?id=25615

diff -u -r ../libvorbis-1.3.5/configure ./configure
--- ../libvorbis-1.3.5/configure	2015-02-26 23:09:49.000000000 +0100
+++ ./configure	2017-01-22 23:48:11.744025641 +0100
@@ -12685,7 +12685,7 @@
 	case $host in
 	*86-*-linux*)
 		DEBUG="-g -Wall -Wextra -D_REENTRANT -D__NO_MATH_INLINES -fsigned-char"
-		CFLAGS="-O3 -ffast-math -mno-ieee-fp -D_REENTRANT -fsigned-char"
+		CFLAGS="-O3 -ffast-math -D_REENTRANT -fsigned-char"
 #              	PROFILE="-Wall -Wextra -pg -g -O3 -ffast-math -D_REENTRANT -fsigned-char -fno-inline -static"
 		PROFILE="-Wall -Wextra -pg -g -O3 -ffast-math -mno-ieee-fp -D_REENTRANT -fsigned-char -fno-inline"