windows: add windows/386 support

src/internal/task/task_stack_386.S

@@ -1,7 +1,12 @@
+#ifdef _WIN32
+.global  _tinygo_startTask
+_tinygo_startTask:
+#else // Linux etc
 .section .text.tinygo_startTask
 .global  tinygo_startTask
 .type    tinygo_startTask, %function
 tinygo_startTask:
+#endif
     .cfi_startproc
     // Small assembly stub for starting a goroutine. This is already run on the
     // new stack, with the callee-saved registers already loaded.
@@ -24,12 +29,21 @@ tinygo_startTask:
     addl $4, %esp
 
     // After return, exit this goroutine. This is a tail call.
+    #ifdef _WIN32
+    jmp _tinygo_task_exit
+    #else
     jmp tinygo_task_exit
+    #endif
     .cfi_endproc
 
+#ifdef _WIN32
+.global _tinygo_swapTask
+_tinygo_swapTask:
+#else
 .global tinygo_swapTask
 .type tinygo_swapTask, %function
 tinygo_swapTask:
+#endif
     // This function gets the following parameters:
     movl 4(%esp), %eax // newStack uintptr
     movl 8(%esp), %ecx // oldStack *uintptr

src/runtime/asm_386.S

@@ -1,7 +1,12 @@
+#ifdef _WIN32
+.global _tinygo_scanCurrentStack
+_tinygo_scanCurrentStack:
+#else
 .section .text.tinygo_scanCurrentStack
 .global tinygo_scanCurrentStack
 .type tinygo_scanCurrentStack, %function
 tinygo_scanCurrentStack:
+#endif
     // Sources:
     //   * https://stackoverflow.com/questions/18024672/what-registers-are-preserved-through-a-linux-x86-64-function-call
     //   * https://godbolt.org/z/q7e8dn
@@ -15,7 +20,11 @@ tinygo_scanCurrentStack:
     // Scan the stack.
     subl $8, %esp // adjust the stack before the call to maintain 16-byte alignment
     pushl %esp
+    #ifdef _WIN32
+    calll _tinygo_scanstack
+    #else
     calll tinygo_scanstack
+    #endif
 
     // Restore the stack pointer. Registers do not need to be restored as they
     // were only pushed to be discoverable by the GC.
@@ -23,9 +32,14 @@ tinygo_scanCurrentStack:
     retl
 
 
+#ifdef _WIN32
+.global _tinygo_longjmp
+_tinygo_longjmp:
+#else
 .section .text.tinygo_longjmp
 .global tinygo_longjmp
 tinygo_longjmp:
+#endif
     // Note: the code we jump to assumes eax is set to a non-zero value if we
     // jump from here.
     movl 4(%esp), %eax