StdLib: Add support for AArch64

- Use some files from ARM version.
- Use NetBSD software floating point library to provide floating point
  operations not handled directly by hardware floating point enabled
  GCC compiler.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Harry Liebel <Harry.Liebel@arm.com>
Reviewed-by: Olivier Martin <Olivier.Martin@arm.com>
Reviewed-by: Daryl McDaniel <edk2-lists@mc2research.org>

git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@18118 6f19259b-4bc3-4df7-8a09-765794883524

StdLib/Include/Aarch64/machine/fenv.h

@@ -0,0 +1,39 @@
+/*  $NetBSD: fenv.h,v 1.2 2014/01/29 00:22:09 matt Exp $    */
+
+/*
+ * Based on ieeefp.h written by J.T. Conklin, Apr 28, 1995
+ * Public domain.
+ */
+
+#ifndef _AARCH64_FENV_H_
+#define _AARCH64_FENV_H_
+
+/* AArch64 split FPSCR into two registers FPCR and FPSR */
+typedef struct {
+    unsigned int __fpcr;
+    unsigned int __fpsr;
+} fenv_t;
+typedef int fexcept_t;
+
+#define FE_INVALID      0x01    /* invalid operation exception */
+#define FE_DIVBYZERO    0x02    /* divide-by-zero exception */
+#define FE_OVERFLOW     0x04    /* overflow exception */
+#define FE_UNDERFLOW    0x08    /* underflow exception */
+#define FE_INEXACT      0x10    /* imprecise (loss of precision; "inexact") */
+
+#define FE_ALL_EXCEPT   0x1f
+
+#define FE_TONEAREST    0   /* round to nearest representable number */
+#define FE_UPWARD       1   /* round toward positive infinity */
+#define FE_DOWNWARD     2   /* round toward negative infinity */
+#define FE_TOWARDZERO   3   /* round to zero (truncate) */
+
+__BEGIN_DECLS
+
+/* Default floating-point environment */
+extern const fenv_t __fe_dfl_env;
+#define FE_DFL_ENV  (&__fe_dfl_env)
+
+__END_DECLS
+
+#endif /* _AARCH64_FENV_H_ */