Patch: Assemblers do not handle minimum vlong value correctly.

[Ori Bernstein <ori@eigenstate.org>]

The Plan 9 assemblers use strtoll to parse the integer literals
in their input. It turns out that this is almost correct, but
VLONG_MIN is clamped. This patch changes to use strtoull
in order to allow the full range of integers.

Below is a program that demosntrates the problem:

	term% cat test.s
	GLOBL L2<>+0(SB),$8
		DATA L2<>+0(SB)/8,$-9223372036854775808
		
	TEXT main+0(SB),2,$0
		MOVQ L2<>+0(SB),AX
		RET

	term% 6a test.s
	term% 6l test.6 /amd64/lib/libc.a
	term% acid 6.out
	6.out:amd64 plan 9 executable
	/sys/lib/acid/port
	/sys/lib/acid/amd64
	acid: new()
	33489: overflow	_main	SUBQ	$0x90,SP
	33489: breakpoint	main+0x8	RET
	acid: *L2
	0x8000000000000001
	acid: -9223372036854775808
	0x8000000000000000

And the patch:


	diff -r a01d0802d023 sys/src/cmd/cc/lexbody
	--- a/sys/src/cmd/cc/lexbody	Mon Mar 20 19:15:40 2017 +0100
	+++ b/sys/src/cmd/cc/lexbody	Tue Mar 21 21:45:44 2017 -0700
	@@ -343,10 +343,9 @@
				goto casee;
			*cp = 0;
			if(sizeof(yylval.lval) == sizeof(vlong))
	-			yylval.lval = strtoll(symb, nil, 10);
	+			yylval.lval = strtoull(symb, nil, 10);
			else
	-			yylval.lval = strtol(symb, nil, 10);
	-
	+			yylval.lval = strtoul(symb, nil, 10);
		ncu:
			while(c == 'U' || c == 'u' || c == 'l' || c == 'L')
				c = GETC();

-- 
    Ori Bernstein