Disallow SECTION UNION for ROM sections

Fixes #1855

test/asm/fragment-literal-in-union.err

@@ -1,2 +1,6 @@
-FATAL: `SECTION UNION` cannot contain fragment literals
+error: Cannot declare ROM sections as `UNION`
+    at fragment-literal-in-union.asm(1)
+error: Cannot output data outside of a `SECTION`
+    at fragment-literal-in-union.asm(2)
+FATAL: Cannot output fragment literals outside of a `SECTION`
     at fragment-literal-in-union.asm(3)

test/asm/section-union-data.asm

@@ -0,0 +1,2 @@
+SECTION UNION "wat", ROM0
+db 42

test/asm/section-union-data.err

@@ -0,0 +1,5 @@
+error: Cannot declare ROM sections as `UNION`
+    at section-union-data.asm(1)
+error: Cannot output data outside of a `SECTION`
+    at section-union-data.asm(2)
+Assembly aborted with 2 errors!

test/link/section-conflict/different-mod/a.asm

@@ -1,2 +1,2 @@
-section fragment "test", rom0
-db 1
+section fragment "test", wram0
+w1:: db

test/link/section-conflict/different-mod/b.asm

@@ -1,2 +1,2 @@
-section union "test", rom0
-db 2
+section union "test", wram0
+w2:: db

test/link/section-union/data-overlay.asm

@@ -1,10 +0,0 @@
-IF !DEF(SECOND)
-	def DATA equs "ds 4"
-ELSE
-	def DATA equs "db $aa, $bb, $cc, $dd"
-ENDC
-
-SECTION UNION "overlaid data", ROM0
-	{DATA}
-
-	PURGE DATA

test/link/section-union/data-overlay.out

@@ -1,7 +0,0 @@
-FATAL: Section "overlaid data" is of type `ROM0`, which cannot be `UNION`ized
-Linking aborted with 1 error
----
-error: Cannot declare ROM sections as `UNION`
-    at <stdin>(18)
-FATAL: Cannot create section "overlaid data" (1 error)
-    at <stdin>(18)

test/link/section-union/different-data.asm

@@ -1,8 +0,0 @@
-IF !DEF(SECOND)
-	def DATA = 1
-ELSE
-	def DATA = 2
-ENDC
-
-SECTION UNION "different data", ROM0
-	db DATA

test/link/section-union/different-data.out

@@ -1,7 +0,0 @@
-FATAL: Section "different data" is of type `ROM0`, which cannot be `UNION`ized
-Linking aborted with 1 error
----
-error: Cannot declare ROM sections as `UNION`
-    at <stdin>(16)
-FATAL: Cannot create section "different data" (1 error)
-    at <stdin>(16)

test/link/section-union/different-size.asm

@@ -1,8 +0,0 @@
-IF !DEF(SECOND)
-	def SIZE = 69
-ELSE
-	def SIZE = 420
-ENDC
-
-SECTION UNION "different section sizes", ROM0
-	ds SIZE

test/link/section-union/different-size.out

@@ -1,7 +0,0 @@
-FATAL: Section "different section sizes" is of type `ROM0`, which cannot be `UNION`ized
-Linking aborted with 1 error
----
-error: Cannot declare ROM sections as `UNION`
-    at <stdin>(16)
-FATAL: Cannot create section "different section sizes" (1 error)
-    at <stdin>(16)

test/link/section-union/different-syntaxes.asm

@@ -1,10 +0,0 @@
-IF !DEF(SECOND)
-	def INSTR equs "sbc a"
-ELSE
-	def INSTR equs "db $9f"
-ENDC
-
-SECTION UNION "different syntaxes", ROM0
-	{INSTR}
-
-	PURGE INSTR

test/link/section-union/different-syntaxes.out

@@ -1,7 +0,0 @@
-FATAL: Section "different syntaxes" is of type `ROM0`, which cannot be `UNION`ized
-Linking aborted with 1 error
----
-error: Cannot declare ROM sections as `UNION`
-    at <stdin>(18)
-FATAL: Cannot create section "different syntaxes" (1 error)
-    at <stdin>(18)

test/link/section-union/split-data.asm

@@ -1,10 +0,0 @@
-IF !DEF(SECOND)
-	def DATA equs "ds 1\ndb $aa"
-ELSE
-	def DATA equs "db $bb\nds 1"
-ENDC
-
-SECTION UNION "mutually-overlaid data", ROM0
-	{DATA}
-
-	PURGE DATA

test/link/section-union/split-data.out

@@ -1,7 +0,0 @@
-FATAL: Section "mutually-overlaid data" is of type `ROM0`, which cannot be `UNION`ized
-Linking aborted with 1 error
----
-error: Cannot declare ROM sections as `UNION`
-    at <stdin>(18)
-FATAL: Cannot create section "mutually-overlaid data" (1 error)
-    at <stdin>(18)