Use llvm-cov in macos CI

.github/build.sh

@@ -43,6 +43,9 @@ case "${CC:-gcc}" in
 		lcov --list lcov-coverage.txt
 		;;
 	clang)
+		if [[ x$(uname) == xDarwin ]]; then
+			export PATH=$PATH:/Library/Developer/CommandLineTools/usr/bin
+		fi
 		llvm-profdata merge unittest.profraw -o unittest.profdata
 		llvm-profdata merge inttest.profraw -o inttest.profdata
 		llvm-cov show -show-line-counts-or-regions -instr-profile=unittest.profdata test/unittest_bin > unittest-cmake-coverage.txt

.github/workflows/build.yml

@@ -103,6 +103,10 @@ jobs:
   macos:
     name: macOS
     runs-on: macos-latest
+    env:
+      # This doesn't make big difference, since it's the same compiler, but we also use this variable to select lcov vs llvm-cov
+      CXX: clang++
+      CC: clang
     steps:
       - uses: actions/checkout@v3
         with: