Remove undefined behavior from shifts

`asl` and `asr` in `src/link/patch.c` courtesy of @pinobatch, and rearranged in RGBASM
evaluators.

test/asm/shift.asm

@@ -0,0 +1,27 @@
+test: macro
+	; Test the rpn system, as well as the linker...
+	dl \1 + zero
+
+	; ...as well as the constexpr system
+result\@ equ \1
+	printt "\1 = {result\@}\n"
+endm
+
+section "test", ROM0[0]
+
+	test 1 << 1
+	test 1 << 32
+	test 1 << 9001
+	test -1 << 1
+	test -1 << 32
+	test -1 << -9001
+
+	test -1 >> 1
+	test -1 >> 32
+	test -1 >> 9001
+	test -4 >> 1
+	test -4 >> 2
+	test -1 >> -9001
+
+SECTION "Zero", ROM0[0]
+zero: