Avoid testcase build failures with -Wunused-value

Avoid testcase build failures with -Wunused-value

A number of testcases fail to build with -Wunused-value enabled.
This commit adds dummy values to avoid this.

gdb/testsuite/ChangeLog:

	* gdb.cp/namespace.cc: Avoid build failure with -Wunused-value.
	* gdb.cp/nsimport.cc: Likewise.
	* gdb.cp/nsnested.cc: Likewise.
	* gdb.cp/nsnoimports.cc: Likewise.
	* gdb.cp/nsusing.cc: Likewise.
	* gdb.cp/smartp.cc: Likewise.
	* gdb.python/py-pp-integral.c: Likewise.
	* gdb.python/py-pp-re-notag.c: Likewise.