gdb/fortran: better types for components of complex numbers

gdb/fortran: better types for components of complex numbers

Currently when using $_creal and $_cimag to access the components of a
complex number the types of these components will have C type names
'float', 'double', etc.  This is because the components of a complex
number are not given type names in DWARF, so GDB has to pick some
suitable names, and currently we always use the C names.

This commit changes the type names used based on the language, so for
Fortran we will now use the Fortran float types, and so will get the
Fortran float type names 'real', 'real*8', etc.

gdb/ChangeLog:

	* dwarf2read.c (dwarf2_init_complex_target_type): Use different
	types for Fortran.

gdb/testsuite/ChangeLog:

	* gdb.fortran/complex.exp: Expand.
	* gdb.fortran/complex.f: Renamed to...
	* gdb.fortran/complex.f90: ...this, and extended to add more
	complex values.