Add missing long double functions to Cygwin

This patch adds the long double functions missing in newlib to Cygwin.
Apart from some self-written additions (exp10l, finite{f,l}, isinf{f,l},
isnan{f,l}, pow10l) the files are taken from the Mingw-w64 math lib.
Minor changes were required, e.g. substitue _WIN64 with __x86_64__ and
fixing __FLT_RPT_DOMAIN/__FLT_RPT_ERANGE for Cygwin.

Cygwin:
	* math: New subdir with math functions.
	* Makefile.in (VPATH): Add math subdir.
	(MATH_OFILES): List of object files collected from building files in
	math subdir.
	(DLL_OFILES): Add $(MATH_OFILES).
	${CURDIR}/libm.a: Add $(MATH_OFILES) to build.
	* common.din: Add new functions from math subdir.
	* i686.din: Align to new math subdir.  Remove functions now commonly
	available.
	* x86_64.din: Ditto.
	* math.h: math.h wrapper to define mingw structs used in some files in
	math subdir.
	* include/cygwin/version.h: Bump API minor version.

newlib:
	* libc/include/complex.h: Add prototypes for complex long double
	functions.  Only define for Cygwin.
	* libc/include/math.h: Additionally enable prototypes of long double
	functions for Cygwin.  Add Cygwin-only prototypes for dreml, sincosl,
	exp10l and pow10l.  Explain why we don't add them to newlib.
	* libc/include/tgmath.h: Enable long double handling on Cygwin.

Signed-off-by: Corinna Vinschen <corinna@vinschen.de>

winsup/cygwin/math/cbrtl.c

@@ -0,0 +1,80 @@
+/**
+ * This file has no copyright assigned and is placed in the Public Domain.
+ * This file is part of the mingw-w64 runtime package.
+ * No warranty is given; refer to the file DISCLAIMER.PD within this package.
+ */
+#include <math.h>
+
+static const long double CBRT2  = 1.2599210498948731647672L;
+static const long double CBRT4  = 1.5874010519681994747517L;
+static const long double CBRT2I = 0.79370052598409973737585L;
+static const long double CBRT4I = 0.62996052494743658238361L;
+
+long double cbrtl(long double x)
+{
+	int e, rem, sign;
+	long double z;
+
+	if (!isfinite (x) || x == 0.0L)
+		return (x);
+
+	if (x > 0)
+		sign = 1;
+	else
+	{
+		sign = -1;
+		x = -x;
+	}
+
+	z = x;
+	/* extract power of 2, leaving
+	 * mantissa between 0.5 and 1
+	 */
+	x = frexpl(x, &e);
+
+	/* Approximate cube root of number between .5 and 1,
+	 * peak relative error = 1.2e-6
+	 */
+	x = (((( 1.3584464340920900529734e-1L * x
+	       - 6.3986917220457538402318e-1L) * x
+	       + 1.2875551670318751538055e0L) * x
+	       - 1.4897083391357284957891e0L) * x
+	       + 1.3304961236013647092521e0L) * x
+	       + 3.7568280825958912391243e-1L;
+
+	/* exponent divided by 3 */
+	if (e >= 0)
+	{
+		rem = e;
+		e /= 3;
+		rem -= 3*e;
+		if (rem == 1)
+			x *= CBRT2;
+		else if (rem == 2)
+			x *= CBRT4;
+	}
+	else
+	{ /* argument less than 1 */
+		e = -e;
+		rem = e;
+		e /= 3;
+		rem -= 3*e;
+		if (rem == 1)
+			x *= CBRT2I;
+		else if (rem == 2)
+			x *= CBRT4I;
+		e = -e;
+	}
+
+	/* multiply by power of 2 */
+	x = ldexpl(x, e);
+
+	/* Newton iteration */
+
+	x -= ( x - (z/(x*x)) )*0.3333333333333333333333L;
+	x -= ( x - (z/(x*x)) )*0.3333333333333333333333L;
+
+	if (sign < 0)
+		x = -x;
+	return (x);
+}