Add legacy inlines for fenv APIs.

Test: make native
      Copied into the NDK and ran ndk/checkbuild.py
Bug: None

Change-Id: I3d1e9317952ad23145a1f5221e347a16ebad4b0d
diff --git a/libc/include/fenv.h b/libc/include/fenv.h
index f1b2b25..241e845 100644
--- a/libc/include/fenv.h
+++ b/libc/include/fenv.h
@@ -36,6 +36,7 @@
 __BEGIN_DECLS
 
 // fenv was always available on x86.
+#if __ANDROID_API__ >= 21 || 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);
@@ -56,6 +57,9 @@
 int feenableexcept(int) __INTRODUCED_IN_ARM(21) __INTRODUCED_IN_MIPS(21) __INTRODUCED_IN_X86(9);
 int fedisableexcept(int) __INTRODUCED_IN_ARM(21) __INTRODUCED_IN_MIPS(21) __INTRODUCED_IN_X86(9);
 int fegetexcept(void) __INTRODUCED_IN_ARM(21) __INTRODUCED_IN_MIPS(21) __INTRODUCED_IN_X86(9);
+#else
+/* Defined as inlines for pre-21 ARM and MIPS. */
+#endif
 
 /*
  * The following constant represents the default floating-point environment
@@ -70,4 +74,7 @@
 
 __END_DECLS
 
+#include <android/legacy_fenv_inlines_arm.h>
+#include <android/legacy_fenv_inlines_mips.h>
+
 #endif  /* ! _FENV_H_ */