gas: Fix a testcase broken by new ZSTD support

The commit 1369522 ("Recognize the new ELF
compression type for ZSTD.") added the new ELF compression type but it
accidentally broke a GAS testcase.  Since testing for the section type
"2048" (SHF_COMPRESSED) is not going to be portable in the long term, it
now tests SHF_STRINGS ("32") instead.  ".word 0" should be okay to
represent no null-terminated strings.

gas/ChangeLog:

	* testsuite/gas/elf/section10.s: Use SHF_STRINGS to test.  Put an
	empty string in it.
	* testsuite/gas/elf/section10.d: Reflect the changes above.

gas/testsuite/gas/elf/section10.d

@@ -13,8 +13,7 @@
 [ 	]*\[.*6000000\]: OS \(.*6000000\)
 [ 	]*\[.*\][ 	]+sec2
 [ 	]*PROGBITS.*
-[ 	]*\[0+00806\]: ALLOC, EXEC, COMPRESSED
-[ 	]*\[<unknown>: 0x[0-9]+\], .*
+[ 	]*\[0+00026\]: ALLOC, EXEC, STRINGS
 #...
 [ 	]*\[.*\][ 	]+sec3
 [ 	]*PROGBITS.*

gas/testsuite/gas/elf/section10.s

@@ -3,8 +3,8 @@
 	.word 1
 
 	# Make sure that a numeric value can be mixed with alpha values.
-	.section sec2, "a2048x"
-	.word 2
+	.section sec2, "a32x"
+	.word 0
 
 	# Make sure that specifying further arguments to .sections is still supported
 	.section sec3, "0xfedff000MS", %progbits, 32