runtime: delete windows setlasterror (unused)

This is dead code and need not be ported to each architecture.

This CL is part of a stack adding windows/arm64
support (#36439), intended to land in the Go 1.17 cycle.
This CL is, however, not windows/arm64-specific.
It is cleanup meant to make the port (and future ports) easier.

Change-Id: I2d0072b377f73e49d7158ea304670c26f5486c59
Reviewed-on: https://go-review.googlesource.com/c/go/+/288794
Trust: Russ Cox <[email protected]>
Trust: Jason A. Donenfeld <[email protected]>
Reviewed-by: Alex Brainman <[email protected]>
Reviewed-by: Cherry Zhang <[email protected]>
Reviewed-by: Jason A. Donenfeld <[email protected]>

Author: rsc

src/runtime/os_windows.go

@@ -379,7 +379,6 @@ const (
 // in sys_windows_386.s and sys_windows_amd64.s:
 func externalthreadhandler()
 func getlasterror() uint32
-func setlasterror(err uint32)
 
 // When loading DLLs, we prefer to use LoadLibraryEx with
 // LOAD_LIBRARY_SEARCH_* flags, if available. LoadLibraryEx is not

src/runtime/sys_windows_386.s

@@ -66,11 +66,6 @@ TEXT runtime·getlasterror(SB),NOSPLIT,$0
 	MOVL	AX, ret+0(FP)
 	RET
 
-TEXT runtime·setlasterror(SB),NOSPLIT,$0
-	MOVL	err+0(FP), AX
-	MOVL	AX, 0x34(FS)
-	RET
-
 // Called by Windows as a Vectored Exception Handler (VEH).
 // First argument is pointer to struct containing
 // exception record and context pointers.

src/runtime/sys_windows_amd64.s

@@ -103,12 +103,6 @@ TEXT runtime·getlasterror(SB),NOSPLIT,$0
 	MOVL	AX, ret+0(FP)
 	RET
 
-TEXT runtime·setlasterror(SB),NOSPLIT,$0
-	MOVL	err+0(FP), AX
-	MOVQ	0x30(GS),	CX
-	MOVL	AX, 0x68(CX)
-	RET
-
 // Called by Windows as a Vectored Exception Handler (VEH).
 // First argument is pointer to struct containing
 // exception record and context pointers.

src/runtime/sys_windows_arm.s

@@ -103,11 +103,6 @@ TEXT runtime·getlasterror(SB),NOSPLIT,$0
 	MOVW	R0, ret+0(FP)
 	RET
 
-TEXT runtime·setlasterror(SB),NOSPLIT|NOFRAME,$0
-	MRC	15, 0, R1, C13, C0, 2
-	MOVW	R0, 0x34(R1)
-	RET
-
 // Called by Windows as a Vectored Exception Handler (VEH).
 // First argument is pointer to struct containing
 // exception record and context pointers.