--- spack-src/configure.org	2019-12-05 10:58:07.408584611 +0900
+++ spack-src/configure	2019-12-05 10:58:29.670909716 +0900
@@ -3019,7 +3019,7 @@
 
 
 # Checks for programs.
-: ${CFLAGS=-O3 -std=c99 -Wall}
+: ${CFLAGS=-O2 -std=c99 -Wall}
 ac_ext=c
 ac_cpp='$CPP $CPPFLAGS'
 ac_compile='$CC -c $CFLAGS $CPPFLAGS conftest.$ac_ext >&5'