Introduce c_value_print_inner

Introduce c_value_print_inner

This introduces c_value_print_inner, which implements the
la_value_print_inner method for the C family of languages.  In this
patch, it is just a simple wrapper of c_val_print.  However,
subsequent patches will convert it to use the value API.  The
transformation is done this way to make each patch easier to review.

Future patches will apply this same treatment to other languages as
well.

gdb/ChangeLog
2020-03-13  Tom Tromey  <tom@tromey.com>

	* opencl-lang.c (opencl_language_defn): Use c_value_print_inner.
	* objc-lang.c (objc_language_defn): Use c_value_print_inner.
	* c-valprint.c (c_value_print_inner): New function.
	* c-lang.h (c_value_print_inner): Declare.
	* c-lang.c (c_language_defn, cplus_language_defn)
	(asm_language_defn, minimal_language_defn): Use
	c_value_print_inner.