x86/entry/entry_32: Route int3 through common_exception

int3 is not using the common_exception path for purely historical reasons,
but there is no reason to keep it the only exception which is different.

Make it use common_exception so the upcoming changes to autogenerate the
entry stubs do not have to special case int3.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Reviewed-by: Alexandre Chartre <alexandre.chartre@oracle.com>
Reviewed-by: Andy Lutomirski <luto@kernel.org>
Link: https://lkml.kernel.org/r/20200225220217.042369808@linutronix.de

arch/x86/entry/entry_32.S

@@ -1683,14 +1683,8 @@ SYM_CODE_END(nmi)
 SYM_CODE_START(int3)
 	ASM_CLAC
 	pushl	$-1				# mark this as an int
-
-	SAVE_ALL switch_stacks=1
-	ENCODE_FRAME_POINTER
-	TRACE_IRQS_OFF
-	xorl	%edx, %edx			# zero error code
-	movl	%esp, %eax			# pt_regs pointer
-	call	do_int3
-	jmp	ret_from_exception
+	pushl	$do_int3
+	jmp	common_exception
 SYM_CODE_END(int3)
 
 SYM_CODE_START(general_protection)