gdb/selftest.m4: ensure $development is set

gdb/selftest.m4: ensure $development is set

Before commit 3d1e5a43cbe ("gdbsupport/configure.ac: source
development.sh"), the GDB build in non-development mode (turn
development to false in bfd/development.sh if you want to try) was
broken because the gdbsupport configure script didn't source
bfd/development.sh to set the development variable.

Since the GDB_AC_SELFTEST macro relies on the `development` variable, I
propose to modify it such that it errors out if $development does not
have an expected value of "true" or "false".  This could prevent a
future similar problem from happening while refactoring the configure
scripts.  It would have caught the problem fixed by the patch mentioned
earlier.

gdb/ChangeLog:

	* selftest.m4 (GDB_AC_SELFTEST): Error out if $development is
	not "true" or "false".
	* configure: Re-generate.

gdbserver/ChangeLog:

	* configure: Re-generate.

gdbsupport/ChangeLog:

	* configure: Re-generate.