Fix fenv_t initializer (#308)

loongarch64/fenv.c

@@ -1,5 +1,5 @@
 #define	__fenv_static
-#include <fenv.h>
+#include <openlibm_fenv.h>
 
 #ifdef __GNUC_GNU_INLINE__
 #error "This file must be compiled with C99 'inline' semantics"

riscv64/fenv.c

@@ -27,7 +27,7 @@
  */
 
 #define	__fenv_static
-#include "fenv.h"
+#include <openlibm_fenv.h>
 
 #ifdef __GNUC_GNU_INLINE__
 #error "This file must be compiled with C99 'inline' semantics"