Testsuite: Remove pie from trace tests

Testsuite: Remove pie from trace tests

Ubuntu/Debian defaults PIE to enabled.  This causes the trace tests
to fall over due to variables being returned as "unavailable".  The
tests were never designed to work with pie.

Simply ensure the nopie flag is always used for the failing tests.

This removes 100+ failures when running native-gdbserver on Ubuntu 18.04.

gdb/testsuite/ChangeLog:

	* gdb.trace/backtrace.exp: Use nopie flag.
	* gdb.trace/circ.exp: Likewise.
	* gdb.trace/collection.exp: Likewise.
	* gdb.trace/ftrace.exp: Likewise.
	* gdb.trace/mi-trace-unavailable.exp: Likewise.
	* gdb.trace/mi-traceframe-changed.exp: Likewise.
	* gdb.trace/qtro.exp: Likewise.
	* gdb.trace/read-memory.exp: Likewise.
	* gdb.trace/report.exp: Likewise.
	* gdb.trace/tfile.exp: Likewise.
	* gdb.trace/tfind.exp: Likewise.
	* gdb.trace/unavailable.exp: Likewise.