microblaze port

based on initial work by rdp, with heavy modifications. some features
including threads are untested because qemu app-level emulation seems
to be broken and I do not have a proper system image for testing.

arch/microblaze/bits/float.h

@@ -0,0 +1,16 @@
+#define FLT_ROUNDS 1
+#define FLT_EVAL_METHOD 0
+
+#define LDBL_MIN 2.2250738585072014e-308
+#define LDBL_MAX 1.7976931348623157e+308
+#define LDBL_EPSILON 2.2204460492503131e-16
+
+#define LDBL_MANT_DIG 53
+#define LDBL_MIN_EXP (-1021)
+#define LDBL_MAX_EXP 1024
+
+#define LDBL_DIG 15
+#define LDBL_MIN_10_EXP (-307)
+#define LDBL_MAX_10_EXP 308
+
+#define DECIMAL_DIG 17