[testsuite] @progbits -> %progbits

[testsuite] @progbits -> %progbits

The ARM assembler has "@" as a comment character, so there are compile
errors in {py,scm}-section-script.c,

 gdb compile failed, /tmp/ccHEzYqy.s: Assembler messages:
 /tmp/ccHEzYqy.s:19: Error: junk at end of line, first unrecognized character is `,'
 /tmp/ccHEzYqy.s:24: Error: junk at end of line, first unrecognized character is `,'
 /tmp/ccHEzYqy.s:29: Error: junk at end of line, first unrecognized character is `,'
 /tmp/ccHEzYqy.s:41: Error: junk at end of line, first unrecognized character is `,'

This patch replaces @progbits with %progbits.

gdb/testsuite:

2016-01-18  Yao Qi  <yao.qi@linaro.org>

	* gdb.guile/scm-section-script.c: Replace @progbits with
	%progbits.
	* gdb.python/py-section-script.c: Likewise.