runtime: change int32 to intgo in findnull and findnullw

Update #6046.
This CL just does findnull and findnullw. There are other functions
to fix but doing them a few at a time will help isolate any (unlikely)
breakages these changes bring up in architectures I can't test
myself.

R=golang-dev, dsymonds
CC=golang-dev
https://golang.org/cl/12520043
diff --git a/src/pkg/runtime/env_plan9.c b/src/pkg/runtime/env_plan9.c
index 0483d7e..599319c 100644
--- a/src/pkg/runtime/env_plan9.c
+++ b/src/pkg/runtime/env_plan9.c
@@ -8,7 +8,8 @@
 byte*
 runtime·getenv(int8 *s)
 {
-	int32 fd, len, n, r;
+	int32 fd, n, r;
+	intgo len;
 	byte file[128];
 	byte *p;
 
diff --git a/src/pkg/runtime/env_posix.c b/src/pkg/runtime/env_posix.c
index 8333811..58da085 100644
--- a/src/pkg/runtime/env_posix.c
+++ b/src/pkg/runtime/env_posix.c
@@ -11,7 +11,8 @@
 byte*
 runtime·getenv(int8 *s)
 {
-	int32 i, j, len;
+	int32 i, j;
+	intgo len;
 	byte *v, *bs;
 	String* envv;
 	int32 envc;
diff --git a/src/pkg/runtime/os_plan9.c b/src/pkg/runtime/os_plan9.c
index e8e116f..52460c7 100644
--- a/src/pkg/runtime/os_plan9.c
+++ b/src/pkg/runtime/os_plan9.c
@@ -194,7 +194,8 @@
 int32
 runtime·postnote(int32 pid, int8* msg)
 {
-	int32 fd, len;
+	int32 fd;
+	intgo len;
 	uint8 buf[128];
 	uint8 tmp[16];
 	uint8 *p, *q;
diff --git a/src/pkg/runtime/os_plan9_386.c b/src/pkg/runtime/os_plan9_386.c
index a174771..0844d72 100644
--- a/src/pkg/runtime/os_plan9_386.c
+++ b/src/pkg/runtime/os_plan9_386.c
@@ -32,7 +32,7 @@
 	Ureg *ureg;
 	uintptr *sp;
 	SigTab *sig, *nsig;
-	int32 len, i;
+	intgo len, i;
 
 	if(!s)
 		return NCONT;
diff --git a/src/pkg/runtime/os_plan9_amd64.c b/src/pkg/runtime/os_plan9_amd64.c
index 30f31e9..58822ff 100644
--- a/src/pkg/runtime/os_plan9_amd64.c
+++ b/src/pkg/runtime/os_plan9_amd64.c
@@ -40,7 +40,7 @@
 	Ureg *ureg;
 	uintptr *sp;
 	SigTab *sig, *nsig;
-	int32 len, i;
+	intgo i, len;
 
 	if(!s)
 		return NCONT;
diff --git a/src/pkg/runtime/print.c b/src/pkg/runtime/print.c
index 5b60159..9220762 100644
--- a/src/pkg/runtime/print.c
+++ b/src/pkg/runtime/print.c
@@ -12,7 +12,7 @@
 // write to goroutine-local buffer if diverting output,
 // or else standard error.
 static void
-gwrite(void *v, int32 n)
+gwrite(void *v, intgo n)
 {
 	if(g == nil || g->writebuf == nil) {
 		runtime·write(2, v, n);
diff --git a/src/pkg/runtime/runtime.c b/src/pkg/runtime/runtime.c
index a0e9a19..7f69358 100644
--- a/src/pkg/runtime/runtime.c
+++ b/src/pkg/runtime/runtime.c
@@ -393,7 +393,7 @@
 runtime·parsedebugvars(void)
 {
 	byte *p;
-	int32 i, n;
+	intgo i, n;
 
 	p = runtime·getenv("GODEBUG");
 	if(p == nil)
diff --git a/src/pkg/runtime/runtime.h b/src/pkg/runtime/runtime.h
index e48b58a..ff3ecfa 100644
--- a/src/pkg/runtime/runtime.h
+++ b/src/pkg/runtime/runtime.h
@@ -717,8 +717,8 @@
  */
 int32	runtime·strcmp(byte*, byte*);
 byte*	runtime·strstr(byte*, byte*);
-int32	runtime·findnull(byte*);
-int32	runtime·findnullw(uint16*);
+intgo	runtime·findnull(byte*);
+intgo	runtime·findnullw(uint16*);
 void	runtime·dump(byte*, int32);
 int32	runtime·runetochar(byte*, int32);
 int32	runtime·charntorune(int32*, uint8*, int32);
diff --git a/src/pkg/runtime/string.goc b/src/pkg/runtime/string.goc
index 15d690a..dccb971 100644
--- a/src/pkg/runtime/string.goc
+++ b/src/pkg/runtime/string.goc
@@ -10,10 +10,10 @@
 
 String	runtime·emptystring;
 
-int32
+intgo
 runtime·findnull(byte *s)
 {
-	int32 l;
+	intgo l;
 
 	if(s == nil)
 		return 0;
@@ -22,10 +22,10 @@
 	return l;
 }
 
-int32
+intgo
 runtime·findnullw(uint16 *s)
 {
-	int32 l;
+	intgo l;
 
 	if(s == nil)
 		return 0;