ld: Fixes issue 1899 ("cannot create 8.out.exe")

http://code.google.com/p/go/issues/detail?id=1899

R=rsc, alex.brainman, bsiegert, hectorchu, bradfitz
CC=golang-dev
https://golang.org/cl/4978047

doc/progs/run

@@ -42,9 +42,13 @@ for i in \
 	$GC $i
 done
 
+# Write to temporary file to avoid mingw bash bug.
+TMPFILE="/tmp/gotest3"
+
 function testit {
 	$LD $1.$O
-	x=$(echo $(./$O.out $2 2>&1))  # extra echo canonicalizes
+	./$O.out $2 2>&1 >"$TMPFILE" || true
+	x=$(echo $(cat "$TMPFILE")) # extra echo canonicalizes
 	if [ "$x" != "$3" ]
 	then
 		echo $1 failed: '"'$x'"' is not '"'$3'"'
@@ -53,7 +57,8 @@ function testit {
 
 function testitpipe {
 	$LD $1.$O
-	x=$(echo $(./$O.out | $2 2>&1))  # extra echo canonicalizes
+	./$O.out | $2 2>&1 >"$TMPFILE" || true
+	x=$(echo $(cat "$TMPFILE")) # extra echo canonicalizes
 	if [ "$x" != "$3" ]
 	then
 		echo $1 failed: '"'$x'"' is not '"'$3'"'
@@ -88,4 +93,4 @@ testit server1 "" ""
 testit eff_bytesize "" "1.00YB 9.09TB"
 testit eff_sequence "" "[-1 2 6 16 44]"
 
-rm -f $O.out *.$O
+rm -f $O.out $O.out.exe *.$O "$TMPFILE"

src/cmd/ld/lib.c

@@ -70,7 +70,12 @@ libinit(void)
 	// add goroot to the end of the libdir list.
 	libdir[nlibdir++] = smprint("%s/pkg/%s_%s", goroot, goos, goarch);
 
+	// Unix doesn't like it when we write to a running (or, sometimes,
+	// recently run) binary, so remove the output file before writing it.
+	// On Windows 7, remove() can force the following create() to fail.
+#ifndef _WIN32
 	remove(outfile);
+#endif
 	cout = create(outfile, 1, 0775);
 	if(cout < 0) {
 		diag("cannot create %s", outfile);