re PR rtl-optimization/5878 (gcc 3.1 breaks on C code generated by the Mercury compiler)

re PR rtl-optimization/5878 (gcc 3.1 breaks on C code generated by the Mercury compiler)

	PR 5878
	* config/arc/arc.h, config/cris/cris.h, config/i386/i386.h,
	config/m68k/m68k.h, config/s390/s390.h, config/sparc/sparc.h
	(PIC_OFFSET_TABLE_REGNUM): Conditionalize on flag_pic.

	* config/arm/arm.h config/i386/i386.h, config/m68k/m68k.h,
	config/sparc/sparc.h (CONDITIONAL_REGISTER_USAGE): Set
	PIC_OFFSET_TABLE_REGNUM based on INVALID_REGNUM not flag_pic.

	* config/arc/arc.h (CONDITIONAL_REGISTER_USAGE): New.
	* config/arm/arm.c (arm_pic_register): Init to INVALID_REGNUM.
	(arm_override_options): Set arm_pic_register if TARGET_APCS_STACK
	also.  Don't set it if not flag_pic.
	* config/i386/i386.c (ix86_save_reg): Trust PIC_OFFSET_TABLE_REGNUM
	to be INVALID_REGNUM when not used.

	* gcc.dg/20020312-2.c: New.

From-SVN: r50713