[dev.power64] runtime: fix SigaltstackT definition for power64le

Also updated defs3_linux.go but had to manually edit defs_linux_power64le.h. Will regenerate the file when cgo is working natively on ppc64.

LGTM=austin
R=rsc, austin
CC=golang-codereviews
https://golang.org/cl/158360043

src/runtime/defs3_linux.go

@@ -35,7 +35,7 @@ type Gregset C.elf_gregset_t
 type FPregset C.elf_fpregset_t
 type Vreg C.elf_vrreg_t
 
-type Sigaltstack C.struct_sigaltstack
+type SigaltstackT C.struct_sigaltstack
 
 // PPC64 uses sigcontext in place of mcontext in ucontext.
 // see http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/arch/powerpc/include/uapi/asm/ucontext.h

src/runtime/defs_linux_power64le.h

@@ -147,7 +147,7 @@ enum {
 //typedef struct Usigset Usigset;
 typedef struct Ptregs Ptregs;
 typedef struct Vreg Vreg;
-typedef struct Sigaltstack Sigaltstack;
+typedef struct SigaltstackT SigaltstackT;
 typedef struct Sigcontext Sigcontext;
 typedef struct Ucontext Ucontext;
 
@@ -179,7 +179,7 @@ struct Vreg {
 	uint32	u[4];
 };
 
-struct Sigaltstack {
+struct SigaltstackT {
 	byte	*ss_sp;
 	int32	ss_flags;
 	byte	Pad_cgo_0[4];
@@ -201,7 +201,7 @@ struct Sigcontext {
 struct Ucontext {
 	uint64	uc_flags;
 	Ucontext	*uc_link;
-	Sigaltstack	uc_stack;
+	SigaltstackT	uc_stack;
 	Usigset	uc_sigmask;
 	Usigset	__unused[15];
 	Sigcontext	uc_mcontext;