ci: Split Linux and macOS pipelines

Don't use a single pipeline for everything.

.github/workflows/linux.yml

@@ -1,4 +1,4 @@
-name: Build
+name: Ubuntu
 on:
   push:
     branches-ignore:
@@ -10,7 +10,6 @@ jobs:
       matrix:
         os: 
           - ubuntu-18.04
-          - macos-10.15
         compiler:
           - gcc
           - clang
@@ -19,16 +18,10 @@ jobs:
           - '-Dglx=no'
           - '-Degl=no'
           - '-Dx11=false'
-        exclude:
-          - os: macos-10.15
-            compiler: gcc
     runs-on: ${{ matrix.os }}
     steps:
       - uses: actions/checkout@v2
-      - if: runner.os == 'macOS'
-        run: brew install ninja
-      - if: runner.os == 'Linux'
-        run: >
+      - run: >
           sudo apt-get update &&
           sudo apt-get install --no-install-recommends
           libgl1-mesa-dev
@@ -42,7 +35,4 @@ jobs:
       - run: |
           python -m pip install --upgrade pip
           pip3 install meson
-      - if: runner.os == 'macOS'
-        run: /bin/sh -c "CC=${{ matrix.compiler }} .github/scripts/epoxy-ci-osx.sh ${{ matrix.build-opts }}"
-      - if: runner.os == 'Linux'
-        run: /bin/sh -c "CC=${{ matrix.compiler }} .github/scripts/epoxy-ci-linux.sh ${{ matrix.build-opts }}"
+          /bin/sh -c "CC=${{ matrix.compiler }} .github/scripts/epoxy-ci-linux.sh ${{ matrix.build-opts }}"

.github/workflows/macos.yml

@@ -0,0 +1,26 @@
+name: macOS
+on:
+  push:
+    branches-ignore:
+      - debian
+      - khronos-registry
+jobs:
+  build:
+    strategy:
+      matrix:
+        build-opts:
+          - ''
+          - '-Dglx=no'
+          - '-Degl=no'
+          - '-Dx11=false'
+    runs-on: macos-10.15
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions/setup-python@v2
+        with:
+          python-version: 3.x
+      - run: |
+          brew install ninja
+          python -m pip install --upgrade pip
+          pip3 install meson
+          /bin/sh -c "CC=clang .github/scripts/epoxy-ci-osx.sh ${{ matrix.build-opts }}"