Add RGBLINK truncation warnings for add sp, e8 and ld hl, sp + e8 (#2179)

test/link/signed-byte-bad.asm

@@ -0,0 +1,13 @@
+SECTION "limit", ROM0, ALIGN[8, 128]
+Limit:
+add sp, Limit
+add sp, -Limit
+ld hl, sp + Limit
+ld hl, sp - Limit
+
+SECTION "test", ROMX
+Invalid:
+add sp, Invalid
+add sp, -Invalid
+ld hl, sp + Invalid
+ld hl, sp - Invalid

test/link/signed-byte-bad.out

@@ -0,0 +1,12 @@
+warning: Value $80 is not signed 8-bit [-Wtruncation]
+    at signed-byte-bad.asm(5)
+warning: Value $80 is not signed 8-bit [-Wtruncation]
+    at signed-byte-bad.asm(3)
+warning: Value -$4000 is not signed 8-bit [-Wtruncation]
+    at signed-byte-bad.asm(13)
+warning: Value $4000 is not signed 8-bit [-Wtruncation]
+    at signed-byte-bad.asm(12)
+warning: Value -$4000 is not signed 8-bit [-Wtruncation]
+    at signed-byte-bad.asm(11)
+warning: Value $4000 is not signed 8-bit [-Wtruncation]
+    at signed-byte-bad.asm(10)

test/link/signed-byte.asm

@@ -0,0 +1,6 @@
+SECTION "test", ROM0, ALIGN[8, 127]
+Valid:
+add sp, Valid
+add sp, -Valid
+ld hl, sp + Valid
+ld hl, sp - Valid