gdb/testsuite: Ensure test links in malloc and free

gdb/testsuite: Ensure test links in malloc and free

The test associated with the source file
gdb.base/share-env-with-gdbserver.c relies on calling malloc and free
within the inferior from GDB.  However, as the test source itself
makes no use of these functions, there's no requirement that they be
linked into the test executable.

This commit adds a dummy call to malloc and free to ensure they are
linked into the test executable.

gdb/testsuite/ChangeLog:

	* gdb.base/share-env-with-gdbserver.c (main): Add call to
	malloc/free.