Index: gcc/config/riscv/linux.h
===================================================================
--- a/gcc/config/riscv/linux.h	(revision 257620)
+++ b/gcc/config/riscv/linux.h	(revision 257621)
@@ -47,6 +47,8 @@
 
 #define ICACHE_FLUSH_FUNC "__riscv_flush_icache"
 
+#define CPP_SPEC "%{pthread:-D_REENTRANT}"
+
 #define LINK_SPEC "\
 -melf" XLEN_SPEC "lriscv \
 %{shared} \