[testsuite] Don't skip gdb.dwarf2/pr10770.exp for non-gcc compiler

[testsuite] Don't skip gdb.dwarf2/pr10770.exp for non-gcc compiler

gdb.dwarf2/pr10770.exp can be used for non-gcc compiler, at least clang.
This patch removes the restriction to only use gcc.  If other compilers,
like xlc or icc, can't compile the .c file, test result is not changed.

gdb/testsuite:

2017-11-22  Yao Qi  <yao.qi@linaro.org>

	* gdb.dwarf2/pr10770.exp: Remove code skipping non-gcc
	compiler.