riscv64 <fenv.h>.

Just the interface for now; implementation to come later.

Test: treehugger
Change-Id: Id1f0b158f708ff501b5e13fe92c6736e4507d7b6
diff --git a/libc/include/fenv.h b/libc/include/fenv.h
index 7b775b6..3fd9852 100644
--- a/libc/include/fenv.h
+++ b/libc/include/fenv.h
@@ -35,6 +35,8 @@
 #include <bits/fenv_arm.h>
 #elif defined(__i386__)
 #include <bits/fenv_x86.h>
+#elif defined(__riscv)
+#include <bits/fenv_riscv64.h>
 #elif defined(__x86_64__)
 #include <bits/fenv_x86_64.h>
 #endif