Don't build with -Werror.

Index: lib/x86_64/CMakeLists.txt
--- lib/x86_64/CMakeLists.txt.orig
+++ lib/x86_64/CMakeLists.txt
@@ -87,7 +87,7 @@ if(${LIBPGMATH_SYSTEM_NAME} MATCHES "Linux")
 endif()
 set(FLAGS "${FLAGS}-Wall -W -Wstrict-prototypes -Wwrite-strings ")
 if(NOT ${LIBPGMATH_SYSTEM_NAME} MATCHES "Windows")
-  set(FLAGS "${FLAGS}-Werror ")
+  set(FLAGS "${FLAGS} ")
 endif()
 libmath_add_object_library("${SRCS}" "${FLAGS}" "${DEFINITIONS}" "isoc99")
 
