cmd/[568]l: do not generate PT_TLS on openbsd

The OpenBSD ld.so(1) does not currently support PT_TLS and refuses
to load ELF binaries that contain PT_TLS sections. Do not emit PT_TLS
sections - we will handle this appropriately in runtime/cgo instead.

R=golang-dev, minux.ma, iant
CC=golang-dev
https://golang.org/cl/6846064

src/cmd/5l/asm.c

@@ -1015,7 +1015,10 @@ asmb(void)
 			phsh(ph, sh);
 
 			// .tbss (optional) and TLS phdr
-			if(tlsoffset != 0) {
+			// Do not emit PT_TLS for OpenBSD since ld.so(1) does
+			// not currently support it. This is handled
+			// appropriately in runtime/cgo.
+			if(tlsoffset != 0 && HEADTYPE != Hopenbsd) {
 				ph = newElfPhdr();
 				ph->type = PT_TLS;
 				ph->flags = PF_R;

src/cmd/6l/asm.c

@@ -1116,7 +1116,10 @@ asmb(void)
 			/*
 			 * Thread-local storage segment (really just size).
 			 */
-			if(tlsoffset != 0) {
+			// Do not emit PT_TLS for OpenBSD since ld.so(1) does
+			// not currently support it. This is handled
+			// appropriately in runtime/cgo.
+			if(tlsoffset != 0 && HEADTYPE != Hopenbsd) {
 				ph = newElfPhdr();
 				ph->type = PT_TLS;
 				ph->flags = PF_R;

src/cmd/8l/asm.c

@@ -1179,7 +1179,10 @@ asmb(void)
 			/*
 			 * Thread-local storage segment (really just size).
 			 */
-			if(tlsoffset != 0) {
+			// Do not emit PT_TLS for OpenBSD since ld.so(1) does
+			// not currently support it. This is handled
+			// appropriately in runtime/cgo.
+			if(tlsoffset != 0 && HEADTYPE != Hopenbsd) {
 				ph = newElfPhdr();
 				ph->type = PT_TLS;
 				ph->flags = PF_R;