Add and use constants for the Android API levels.

Test: bionic tests still pass
Change-Id: If1b619cfc9db1d3f5d91f14f2ace71058dca0c4a
diff --git a/libc/include/fenv.h b/libc/include/fenv.h
index 241e845..a4c37e6 100644
--- a/libc/include/fenv.h
+++ b/libc/include/fenv.h
@@ -36,7 +36,7 @@
 __BEGIN_DECLS
 
 // fenv was always available on x86.
-#if __ANDROID_API__ >= 21 || defined(__i386__)
+#if __ANDROID_API__ >= __ANDROID_API_L__ || defined(__i386__)
 int feclearexcept(int) __INTRODUCED_IN_ARM(21) __INTRODUCED_IN_MIPS(21) __INTRODUCED_IN_X86(9);
 int fegetexceptflag(fexcept_t*, int) __INTRODUCED_IN_ARM(21) __INTRODUCED_IN_MIPS(21)
     __INTRODUCED_IN_X86(9);