Latest glibc appears to want linking against -lm as well for dlopen.
diff --git a/configure.ac b/configure.ac
index c4e146a..e03baa2 100644
--- a/configure.ac
+++ b/configure.ac
@@ -62,7 +62,7 @@ AC_FUNC_ALLOCA
have_win32=false
PTHREAD_FLAGS="-pthread"
-DLOPEN_FLAGS="-ldl"
+DLOPEN_FLAGS="-ldl -lm"
OPENCL_FLAGS="-lOpenCL"
WS2_LIBS=""