build, test: Add support for llvm-cov

Makefile.am

@@ -65,7 +65,7 @@ OSX_PACKAGING = $(OSX_DEPLOY_SCRIPT) $(OSX_FANCY_PLIST) $(OSX_INSTALLER_ICONS) \
   $(top_srcdir)/contrib/macdeploy/detached-sig-apply.sh \
   $(top_srcdir)/contrib/macdeploy/detached-sig-create.sh
 
-COVERAGE_INFO = baseline.info \
+COVERAGE_INFO = $(COV_TOOL_WRAPPER) baseline.info \
   test_bitcoin_filtered.info total_coverage.info \
   baseline_filtered.info functional_test.info functional_test_filtered.info \
   test_bitcoin_coverage.info test_bitcoin.info fuzz.info fuzz_coverage.info
@@ -192,7 +192,11 @@ LCOV_FILTER_PATTERN = \
 	-p "src/secp256k1" \
 	-p "depends"
 
-baseline.info:
+$(COV_TOOL_WRAPPER):
+	@echo 'exec $(COV_TOOL) "$$@"' > $(COV_TOOL_WRAPPER)
+	@chmod +x $(COV_TOOL_WRAPPER)
+
+baseline.info: $(COV_TOOL_WRAPPER)
 	$(LCOV) -c -i -d $(abs_builddir)/src -o $@
 
 baseline_filtered.info: baseline.info