Move CI-only check-diff script to .github/

.github/workflows/check-diff.yml

@@ -8,7 +8,7 @@ env:
   CLICOLOR_FORCE: 1
 
 jobs:
-  checkdiff:
+  check-diff:
     runs-on: ubuntu-slim
     steps:
       - name: Clone repo
@@ -20,7 +20,7 @@ jobs:
         run: |
           MERGE_BASE=$(gh api "/repos/{owner}/{repo}/compare/$BASE_SHA...$HEAD_SHA" --jq '.merge_base_commit.sha')
           git fetch origin "$MERGE_BASE"
-          contrib/checkdiff.bash "$MERGE_BASE" | sed -E 's/^/::warning::/'
+          .github/scripts/check-diff.bash "$MERGE_BASE" | sed -E 's/^/::warning::/'
         env:
           BASE_SHA: ${{ github.event.pull_request.base.sha }}
           HEAD_SHA: ${{ github.event.pull_request.head.sha }}

Makefile

@@ -3,7 +3,7 @@
 .SUFFIXES:
 .SUFFIXES: .cpp .y .o
 
-.PHONY: all clean install checkdiff develop debug profile coverage format tidy iwyu wine-shim dist
+.PHONY: all clean install develop debug profile coverage format tidy iwyu wine-shim dist
 
 # User-defined variables
 
@@ -44,9 +44,6 @@ BISON := src/bison.sh
 
 RM := rm -rf
 
-# Used for checking pull requests
-BASE_REF := origin/master
-
 # Rules to build the RGBDS binaries
 
 all: rgbasm rgblink rgbfix rgbgfx
@@ -214,10 +211,6 @@ install: all
 	$Qinstall -m ${MANMODE} ${MANSRC}rgbds.5 ${MANSRC}rgbasm.5 ${MANSRC}rgbasm-old.5 ${MANSRC}rgblink.5 ${DESTDIR}${mandir}/man5/
 	$Qinstall -m ${MANMODE} ${MANSRC}rgbds.7 ${MANSRC}gbz80.7 ${DESTDIR}${mandir}/man7/
 
-# Target used to check for suspiciously missing changed files.
-checkdiff:
-	$Qcontrib/checkdiff.bash `git merge-base HEAD ${BASE_REF}`
-
 # Target used in development to prevent adding new issues to the source code.
 # All warnings are treated as errors to block the compilation and make the
 # continous integration infrastructure return failure.