Change how complex types are printed in C

Change how complex types are printed in C

GCC accepts the "i" suffix for complex numbers.  I think this is nicer
to read than the current output, so this patch changes the C code to
print complex numbers this way.

gdb/ChangeLog
2020-04-01  Tom Tromey  <tom@tromey.com>

	* c-valprint.c (c_decorations): Change complex suffix to "i".

gdb/testsuite/ChangeLog
2020-04-01  Tom Tromey  <tom@tromey.com>

	* gdb.compile/compile.exp: Update.
	* gdb.compile/compile-cplus.exp: Update.
	* gdb.base/varargs.exp: Update.
	* gdb.base/floatn.exp: Update.
	* gdb.base/endianity.exp: Update.
	* gdb.base/callfuncs.exp (do_function_calls): Update.
	* gdb.base/funcargs.exp (complex_args, complex_integral_args)
	(complex_float_integral_args): Update.
	* gdb.base/complex.exp: Update.
	* gdb.base/complex-parts.exp: Update.