This patch started off just by adding if_then_else support in
write_attr_value to be able to write a saner expression for powerpc
tls_gdld_nomark length.  Then I noticed bit-rot in functions used to
calculate insn_default_length, insn_min_length, and length_unit_log
(which are used by the shorten_branches pass).  These functions
don't handle a const_int length value and return an "unknown" status
that isn't used, or in the case of or_attr_value, doesn't need to be
used.  min_attr_value also attempts to return INT_MAX for the
unhandled rtl case, but this can get lost in recursive calls.  I fixed
that problem by returning INT_MIN instead, and translating that to
INT_MAX in the only caller of min_attr_value.

	PR target/88614
	* genattrtab.c (max_attr_value, min_attr_value, or_attr_value):
	Delete "unknownp" parameter.  Adjust callers.  Handle
	CONST_INT, PLUS, MINUS, and MULT.
	(attr_value_aligned): Renamed from or_attr_value.
	(min_attr_value): Return INT_MIN for unhandled rtl case..
	(min_fn): ..and translate to INT_MAX here.
	(write_length_unit_log): Modify to cope without "unknown".
	(write_attr_value): Handle IF_THEN_ELSE.

From-SVN: r267666