fenv: avoid internal includes in user-facing headers

A future cleanup will drastically reduce the set of headers being installed,
and we don't want to install internal headers in particular.

include/openlibm_fenv_sh3eb.h

@@ -30,7 +30,6 @@
 #define	_FENV_H_
 
 #include <stdint.h>
-#include "cdefs-compat.h"
 
 #ifndef	__fenv_static
 #define	__fenv_static	static
@@ -57,7 +56,10 @@ typedef	uint32_t	fexcept_t;
 #define	FE_DOWNWARD	0x0003
 #define	_ROUND_MASK	(FE_TONEAREST | FE_DOWNWARD | \
 			 FE_UPWARD | FE_TOWARDZERO)
-__BEGIN_DECLS
+
+#ifdef __cplusplus
+extern "C" {
+#endif
 
 /* Default floating-point environment */
 extern const fenv_t	__fe_dfl_env;
@@ -89,6 +91,8 @@ int fegetexcept(void);
 
 #endif /* __BSD_VISIBLE */
 
-__END_DECLS
+#ifdef __cplusplus
+}
+#endif
 
 #endif	/* !_FENV_H_ */