[dev.ssa] cmd/compile: 386 port now works

GOARCH=386 SSATEST=1 ./all.bash passes

Caveat: still needs changes to test/ files to use *_ssa.go versions.  I
won't check those changes in with this CL because the builders will
complain as they don't have SSATEST=1.

Mostly minor fixes.

Implement float <-> uint32 in assembly.  It seems the simplest option
for now.

GO386=387 does not work.  That's why I can't make SSA the default for
386 yet.

Change-Id: Ic4d4402104d32bcfb1fd612f5bb6539f9acb8ae0
Reviewed-on: https://go-review.googlesource.com/25119
Reviewed-by: Cherry Zhang <cherryyz@google.com>
diff --git a/src/cmd/compile/internal/gc/builtin/runtime.go b/src/cmd/compile/internal/gc/builtin/runtime.go
index e9316cb..ef7e408 100644
--- a/src/cmd/compile/internal/gc/builtin/runtime.go
+++ b/src/cmd/compile/internal/gc/builtin/runtime.go
@@ -150,8 +150,10 @@
 func uint64mod(uint64, uint64) uint64
 func float64toint64(float64) int64
 func float64touint64(float64) uint64
+func float64touint32(float64) uint32
 func int64tofloat64(int64) float64
 func uint64tofloat64(uint64) float64
+func uint32tofloat64(uint32) float64
 
 func complex128div(num complex128, den complex128) (quo complex128)