Add ISO C99 complex support for doubles.

* include/complex.h: New file.
	* mingwex/complex: New directory.
	* mingwex/complex/cabs.c: New file.
	* mingwex/complex/cacos.c: New file.
	* mingwex/complex/cacosh.c: New file.
	* mingwex/complex/casin.c: New file.
	* mingwex/complex/casinh.c: New file.
	* mingwex/complex/catan.c: New file.
	* mingwex/complex/catanh.c: New file.
	* mingwex/complex/ccos.c: New file.
	* mingwex/complex/ccosh.c: New file.
	* mingwex/complex/cexp.c: New file.
	* mingwex/complex/cimag.c: New file.
	* mingwex/complex/clog.c: New file.
	* mingwex/complex/cpow.c: New file.
	* mingwex/complex/cproj.c: New file.
	* mingwex/complex/creal.c: New file.
	* mingwex/complex/csin.c: New file.
	* mingwex/complex/csinh.c: New file.
	* mingwex/complex/csqrt.c: New file.
	* mingwex/complex/ctan.c: New file.
	* mingwex/complex/ctanh.c: New file.
	* mingwex/Makefile.in (COMPLEX_DISTFILES): New list of
	files.
	(dist): Use it.
	(COMPLEX_OBJS): New list of objects.
	(LIB_OBJS): Include it in the library.

winsup/mingw/mingwex/complex/csqrt.c

@@ -0,0 +1,55 @@
+/*
+   csqrt.c
+   Contributed by Danny Smith
+   2003-10-20
+*/
+
+#include <math.h>
+#include <complex.h>
+
+double complex  csqrt (double complex Z)
+{
+  double complex Res;
+  double t;
+  double x = __real__ Z;
+  double y = __imag__ Z;
+
+  if (y == 0.0)
+    {
+      if (x < 0.0)
+        {
+ 	  __real__ Res = 0.0;
+	  __imag__ Res = sqrt (-x);
+        }
+      else
+        {
+ 	  __real__ Res = sqrt (x);
+	  __imag__ Res = 0.0;
+        }
+    }
+
+  else if (x == 0.0)
+    {
+      t = sqrt(0.5 * fabs (y));
+      __real__ Res = y > 0 ? t : -t;
+      __imag__ Res = t;
+    }
+
+  else
+    {
+      t = sqrt (2.0  * (_hypot (x, y) + fabs (x)));
+      if ( x > 0.0)
+        {	
+          __real__ Res = 0.5 * t;
+          __imag__ Res = y / t;
+        }
+      else
+        {
+	  __real__ Res = fabs ( y / t);
+	  __imag__ Res = (y < 0.0 ? -0.5 : 0.5) * t;
+        }
+    }
+
+  return Res;
+}
+