c++: "" #pragma at BOF [PR108504]

c++: "" #pragma at BOF [PR108504]

Since r11-2095 we pass flags to cp_lexer_get_preprocessor_token, and
cp_lexer_new_main passes C_LEX_STRING_NO_JOIN when lexing most of the
translation unit, but doesn't do that for the very first token; as a
result, if the first token is a string literal, we try to join strings and
get confused if that encounters a pragma.

	PR c++/108504

gcc/cp/ChangeLog:

	* parser.cc (cp_lexer_new_main): Pass C_LEX_STRING_NO_JOIN for first
	token, too.

gcc/testsuite/ChangeLog:

	* g++.dg/ext/pragma1.C: New test.