Fix testcase for PR ld/22471

ASFLAGS should be restored after any modification.  Fixes
metag-linux  +FAIL: Long branch stub
metag-linux  +FAIL: Long branch stub (PIC, app)
mn10300-elf  +FAIL: difference of two same-section symbols where the difference is held in another section
mn10300-elf  +FAIL: relaxation and alignment directives

	PR 22471
	* testsuite/ld-elf/shared.exp: Save and restore ASFLAGS.

ld/ChangeLog

@@ -1,3 +1,8 @@
+2017-11-30  Alan Modra  <amodra@gmail.com>
+
+	PR 22471
+	* testsuite/ld-elf/shared.exp: Save and restore ASFLAGS.
+
 2017-11-29  H.J. Lu  <hongjiu.lu@intel.com>
 
 	PR ld/22471

ld/testsuite/ld-elf/shared.exp

@@ -34,6 +34,8 @@ if ![check_shared_lib_support] {
 # Add $NOPIE_CFLAGS and $NOPIE_LDFLAGS if non-PIE is required.
 global NOPIE_CFLAGS NOPIE_LDFLAGS
 
+set old_ASFLAGS $ASFLAGS
+
 # This target requires extra GAS options when building code for shared
 # libraries.
 set AFLAGS_PIC ""
@@ -221,6 +223,8 @@ if { [check_gc_sections_available] } {
     ]
 }
 
+set ASFLAGS $old_ASFLAGS
+
 # Check to see if the C compiler works
 if { [which $CC] == 0 } {
     return