diff -up ./config.m4.rpm ./config.m4
--- ./config.m4.rpm	2018-04-09 08:54:24.472418287 +0200
+++ ./config.m4	2018-04-09 08:55:26.124761575 +0200
@@ -11,8 +11,8 @@ if test "$PHP_GRPC" != "no"; then
 
   LIBS="-lpthread $LIBS"
 
-  CFLAGS="-Wall -Werror -Wno-parentheses-equality -Wno-unused-value -std=c11 -g -O2"
-  CXXFLAGS="-std=c++11 -fno-exceptions -fno-rtti -g -O2"
+  CFLAGS="$CFLAGS -std=c11"
+  CXXFLAGS="$CXXFLAGS -std=c++11 -fno-exceptions -fno-rtti"
   GRPC_SHARED_LIBADD="-lpthread $GRPC_SHARED_LIBADD"
   PHP_REQUIRE_CXX()
   PHP_ADD_LIBRARY(pthread)