initial commit of the arm port

this port assumes eabi calling conventions, eabi linux syscall
convention, and presence of the kernel helpers at 0xffff0f?0 needed
for threads support. otherwise it makes very few assumptions, and the
code should work even on armv4 without thumb support, as well as on
systems with thumb interworking. the bits headers declare this a
little endian system, but as far as i can tell the code should work
equally well on big endian.

some small details are probably broken; so far, testing has been
limited to qemu/aboriginal linux.

arch/arm/bits/float.h

@@ -0,0 +1,14 @@
+#define FLT_ROUNDS 1
+#define FLT_EVAL_METHOD 2
+
+#define LDBL_MIN     3.3621031431120935063e-4932L
+#define LDBL_MAX     1.1897314953572317650e+4932L
+#define LDBL_EPSILON 1.0842021724855044340e-19L
+
+#define LDBL_MANT_DIG 64
+#define LDBL_MIN_EXP (-16381)
+#define LDBL_MAX_EXP 16384
+
+#define LDBL_DIG 18
+#define LDBL_MIN_10_EXP (-4931)
+#define LDBL_MAX_10_EXP 4932