autload.cc: Avoid clobbering return address in noload on i686

This fixes a long-standing problem when GetProcAddress fails
	to load a function.  The noload code calls SetLastError on
	i686 without saving the edx register.  Starting with Windows 7,
	SetLastError apparently uses $edx and the register is set to
	0x00000000 on return.  So the subsequent `jmp *$edx' in noload
	supposed to return to the caller, actually jumps to address NULL,
	which results in a SEGV.

        * autoload.cc (noload): i686 only: Save and restore $edx when calling
        SetLastError to avoid clobbering return address stating with Windows 7.

Signed-off-by: Corinna Vinschen <corinna@vinschen.de>

winsup/cygwin/ChangeLog

@@ -1,3 +1,8 @@
+2015-08-25  Corinna Vinschen  <corinna@vinschen.de>
+
+	* autoload.cc (noload): i686 only: Save and restore $edx when calling
+	SetLastError to avoid clobbering return address stating with Windows 7.
+
 2015-08-25  Corinna Vinschen  <corinna@vinschen.de>
 
 	* mmap.cc: Fix a few comments.

winsup/cygwin/autoload.cc

@@ -254,11 +254,13 @@ noload:									\n\
 	addl	%eax,%esp	# Pop off bytes				\n\
 	andl	$0xffff0000,%eax# upper word				\n\
 	subl	%eax,%esp	# adjust for possible return value	\n\
-	pushl	%eax		# Save for later			\n\
+	pushl	%eax		# Save return value for later		\n\
+	pushl	%edx		# Save return address for later		\n\
 	movl	$127,%eax	# ERROR_PROC_NOT_FOUND			\n\
 	pushl	%eax		# First argument			\n\
 	call	_SetLastError@4	# Set it				\n\
-	popl	%eax		# Get back argument			\n\
+	popl	%edx		# Get back return address		\n\
+	popl	%eax		# Get back return value			\n\
 	sarl	$16,%eax	# return value in high order word	\n\
 	jmp	*%edx		# Return				\n\
 1:									\n\