cmd/dist, cmd/8g: implement GO386=387/sse to choose FPU flavour.

A new environment variable GO386 is introduced to choose between
code generation targeting 387 or SSE2. No auto-detection is
performed and the setting defaults to 387 to preserve previous
behaviour.

The patch is a reorganization of CL6549052 by rsc.

Fixes issue 3912.

R=minux.ma, rsc
CC=golang-dev
https://codereview.appspot.com/6962043

1 files changed, 6 insertions, 0 deletions

diff --git a/src/lib9/goos.c b/src/lib9/goos.c
index c89275749..3b0027111 100644
--- a/src/lib9/goos.c
+++ b/src/lib9/goos.c
@@ -45,3 +45,9 @@ getgoarm(void)
 {
 	return defgetenv("GOARM", GOARM);
 }
+
+char*
+getgo386(void)
+{
+	return defgetenv("GO386", GO386);
+}