ci: Fix llvm detection on macOS CI

LLVM is keg-only now, so we need to add CPPFLAGS / LDFLAGS to the keg
subdir inside /usr/local

Author: nirbheek

.github/workflows/macos.yml

@@ -36,8 +36,8 @@ jobs:
         python -m pip install pytest pytest-xdist pytest-subtests jsonschema coverage codecov
     - run: brew install pkg-config ninja llvm qt@5
     - env:
-        CPPFLAGS: "-I/usr/local/include"
-        LDFLAGS: "-L/usr/local/lib"
+        CPPFLAGS: "-I/usr/local/include -I/usr/local/opt/llvm/include"
+        LDFLAGS: "-L/usr/local/lib -L/usr/local/opt/llvm/lib"
         MESON_CI_JOBNAME: unittests-appleclang
         MESON_UNIT_TEST_BACKEND: ninja
         # These cannot evaluate anything, so we cannot set PATH or SDKROOT here
@@ -75,8 +75,8 @@ jobs:
         python3 -m pip install --upgrade pip
         python3 -m pip install cython coverage codecov
     - env:
-        CPPFLAGS: "-I/usr/local/include"
-        LDFLAGS: "-L/usr/local/lib"
+        CPPFLAGS: "-I/usr/local/include -I/usr/local/opt/llvm/include"
+        LDFLAGS: "-L/usr/local/lib -L/usr/local/opt/llvm/lib"
         MESON_ARGS: --unity=${{ matrix.unity }}
         CI: 1
         # These cannot evaluate anything, so we cannot set PATH or SDKROOT here