runtime: mark some C globals as having no pointers.

C globals are conservatively scanned.  This helps
avoid false retention, especially for 32 bit.

LGTM=rsc
R=golang-codereviews, khr, rsc
CC=golang-codereviews
https://golang.org/cl/102040043

src/pkg/runtime/alg.goc

@@ -465,6 +465,7 @@ runtime·algarray[] =
 // Runtime helpers.
 
 // used in asm_{386,amd64}.s
+#pragma dataflag NOPTR
 byte runtime·aeskeysched[HashRandomBytes];
 
 void

src/pkg/runtime/heapdump.c

@@ -17,6 +17,7 @@
 #include "typekind.h"
 #include "funcdata.h"
 #include "zaexperiment.h"
+#include "../../cmd/ld/textflag.h"
 
 extern byte data[];
 extern byte edata[];
@@ -67,6 +68,7 @@ static uintptr dumpfd;
 enum {
 	BufSize = 4096,
 };
+#pragma dataflag NOPTR
 static byte buf[BufSize];
 static uintptr nbuf;
 

src/pkg/runtime/malloc.goc

@@ -19,6 +19,7 @@ package runtime
 // Mark mheap as 'no pointers', it does not contain interesting pointers but occupies ~45K.
 #pragma dataflag NOPTR
 MHeap runtime·mheap;
+#pragma dataflag NOPTR
 MStats mstats;
 
 int32	runtime·checking;

src/pkg/runtime/msize.c

@@ -28,8 +28,11 @@
 #include "runtime.h"
 #include "arch_GOARCH.h"
 #include "malloc.h"
+#include "../../cmd/ld/textflag.h"
 
+#pragma dataflag NOPTR
 int32 runtime·class_to_size[NumSizeClasses];
+#pragma dataflag NOPTR
 int32 runtime·class_to_allocnpages[NumSizeClasses];
 
 // The SizeToClass lookup is implemented using two arrays,
@@ -41,7 +44,9 @@ int32 runtime·class_to_allocnpages[NumSizeClasses];
 // size divided by 128 (rounded up).  The arrays are filled in
 // by InitSizes.
 
+#pragma dataflag NOPTR
 int8 runtime·size_to_class8[1024/8 + 1];
+#pragma dataflag NOPTR
 int8 runtime·size_to_class128[(MaxSmallSize-1024)/128 + 1];
 
 void runtime·testdefersizes(void);

src/pkg/runtime/os_darwin.c

@@ -59,6 +59,7 @@ runtime·osinit(void)
 void
 runtime·get_random_data(byte **rnd, int32 *rnd_len)
 {
+	#pragma dataflag NOPTR
 	static byte urandom_data[HashRandomBytes];
 	int32 fd;
 	fd = runtime·open("/dev/urandom", 0 /* O_RDONLY */, 0);

src/pkg/runtime/os_dragonfly.c

@@ -122,6 +122,7 @@ runtime·osinit(void)
 void
 runtime·get_random_data(byte **rnd, int32 *rnd_len)
 {
+	#pragma dataflag NOPTR
 	static byte urandom_data[HashRandomBytes];
 	int32 fd;
 	fd = runtime·open("/dev/urandom", 0 /* O_RDONLY */, 0);

src/pkg/runtime/os_freebsd.c

@@ -130,6 +130,7 @@ runtime·osinit(void)
 void
 runtime·get_random_data(byte **rnd, int32 *rnd_len)
 {
+	#pragma dataflag NOPTR
 	static byte urandom_data[HashRandomBytes];
 	int32 fd;
 	fd = runtime·open("/dev/urandom", 0 /* O_RDONLY */, 0);

src/pkg/runtime/os_netbsd.c

@@ -188,6 +188,7 @@ runtime·osinit(void)
 void
 runtime·get_random_data(byte **rnd, int32 *rnd_len)
 {
+	#pragma dataflag NOPTR
 	static byte urandom_data[HashRandomBytes];
 	int32 fd;
 	fd = runtime·open("/dev/urandom", 0 /* O_RDONLY */, 0);

src/pkg/runtime/os_openbsd.c

@@ -167,6 +167,7 @@ runtime·osinit(void)
 void
 runtime·get_random_data(byte **rnd, int32 *rnd_len)
 {
+	#pragma dataflag NOPTR
 	static byte urandom_data[HashRandomBytes];
 	int32 fd;
 	fd = runtime·open("/dev/urandom", 0 /* O_RDONLY */, 0);

src/pkg/runtime/os_solaris.c

@@ -161,6 +161,7 @@ runtime·newosproc(M *mp, void *stk)
 void
 runtime·get_random_data(byte **rnd, int32 *rnd_len)
 {
+	#pragma dataflag NOPTR
 	static byte urandom_data[HashRandomBytes];
 	int32 fd;
 	fd = runtime·open("/dev/urandom", 0 /* O_RDONLY */, 0);

src/pkg/runtime/proc.c

@@ -2597,6 +2597,7 @@ struct Pdesc
 	uint32	syscalltick;
 	int64	syscallwhen;
 };
+#pragma dataflag NOPTR
 static Pdesc pdesc[MaxGomaxprocs];
 
 static uint32