Use -Werror in Makefile builds in CI only

Warnings as errors interfere with local development, especially Wunused;
for CMake we already switched to specifying werror separately as an
option, and it's probably time to do this for Makefile as well.

.github/workflows/build.yml

@@ -17,6 +17,8 @@ jobs:
         os: [{ name: ubuntu, version: ubuntu-latest }, { name: macos-intel, version: macos-13 }, { name: macos-arm, version: macos-14 }]
     name: ${{matrix.os.name}}
     runs-on: ${{matrix.os.version}}
+    env:
+      werror: 1
     steps:
       - uses: actions/checkout@v4
       - name: work around ASLR+ASAN compatibility
@@ -131,6 +133,8 @@ jobs:
 
   gltfpack-basis:
     runs-on: ubuntu-latest
+    env:
+      werror: 1
     steps:
       - uses: actions/checkout@v4
       - uses: actions/checkout@v4

Makefile

@@ -19,8 +19,8 @@ OBJECTS=$(LIBRARY_OBJECTS) $(DEMO_OBJECTS) $(GLTFPACK_OBJECTS)
 LIBRARY=$(BUILD)/libmeshoptimizer.a
 DEMO=$(BUILD)/meshoptimizer
 
-CFLAGS=-g -Wall -Wextra -Werror -std=c89
-CXXFLAGS=-g -Wall -Wextra -Wshadow -Wno-missing-field-initializers -Werror -std=gnu++98
+CFLAGS=-g -Wall -Wextra -std=c89
+CXXFLAGS=-g -Wall -Wextra -Wshadow -Wno-missing-field-initializers -std=gnu++98
 LDFLAGS=
 
 $(GLTFPACK_OBJECTS): CXXFLAGS+=-std=c++11
@@ -63,6 +63,11 @@ WASM_SIMPLIFIER_EXPORTS=meshopt_simplify meshopt_simplifyWithAttributes meshopt_
 WASM_CLUSTERIZER_SOURCES=src/clusterizer.cpp tools/wasmstubs.cpp
 WASM_CLUSTERIZER_EXPORTS=meshopt_buildMeshletsBound meshopt_buildMeshlets meshopt_computeClusterBounds meshopt_computeMeshletBounds meshopt_optimizeMeshlet sbrk __wasm_call_ctors
 
+ifneq ($(werror),)
+	CFLAGS+=-Werror
+	CXXFLAGS+=-Werror
+endif
+
 ifeq ($(config),iphone)
 	IPHONESDK=/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS.sdk
 	CFLAGS+=-arch armv7 -arch arm64 -isysroot $(IPHONESDK)