modula2: bootstrap fix for string and vector headers.

modula2: bootstrap fix for string and vector headers.

This patch fixes the include of headers (<string> and <vector>) which
are included after GCC's system.h has been included.  It defines
INCLUDE_STRING before including "system.h".  This allows gcc to
bootstrap with Apple clang 15.

gcc/m2/ChangeLog:

	* gm2-gcc/m2linemap.cc (INCLUDE_STRING): Define before
	include of gcc-consolidation.h.
	* gm2spec.cc (INCLUDE_STRING): Define before include of
	system.h.
	(INCLUDE_VECTOR): Ditto.

Signed-off-by: Gaius Mulley <gaiusmod2@gmail.com>