builtins.c, [...]: Say "argument" instead of "arg" in diagnostics.

builtins.c, [...]: Say "argument" instead of "arg" in diagnostics.

	* builtins.c, c-common.c, c-decl.c, c-format.c: Say "argument"
	instead of "arg" in diagnostics.

testsuite:
	* gcc.dg/builtin-prefetch-1.c: Update expected diagnostic.

From-SVN: r90338