[testsuite, Fortran] Consistently set 'DEFAULT_FFLAGS'

[testsuite, Fortran] Consistently set 'DEFAULT_FFLAGS'

In the same 'runtest' instance, 'global' variables persist from one '*.exp'
file to another.

All other '*.exp' files are using " -pedantic-errors" instead of the empty
string as the default for 'DEFAULT_FFLAGS'.  Thus this setting of
'DEFAULT_FFLAGS' is not idempotent, depends on whether
'gfortran.dg/ieee/ieee.exp', or an other defining '*.exp' file is executed
first.

	gcc/testsuite/
	PR fortran/29383
	* gfortran.dg/ieee/ieee.exp (DEFAULT_FFLAGS): Set the same as in
	other '*.exp' files.

From-SVN: r269845