build: don't bother with _LIBCPP_ENABLE_ASSERTIONS

It's a library feature, so the check should be on the libc++ version,
not the compiler. But given that it's already deprecated and superseded
by the hardening mode in newer versions, let's just drop it altogether.

Also, suppress two new errors raised by lcov 2.3.

Change-Id: If17d0a69f910c1c464e9522b04e65102740ccb90
diff --git a/.jenkins.d/30-coverage.sh b/.jenkins.d/30-coverage.sh
index 83edcda..aaab885 100755
--- a/.jenkins.d/30-coverage.sh
+++ b/.jenkins.d/30-coverage.sh
@@ -30,9 +30,9 @@
     --include "$PWD/core/*" \
     --include "$PWD/daemon/*" \
     --include "$PWD/tools/*" \
-    --ignore-errors count,inconsistent \
     --branch-coverage \
     --rc no_exception_branch=1 \
+    --ignore-errors inconsistent,mismatch,mismatch \
     --output-file build/coverage.info
 
 genhtml \
@@ -43,5 +43,6 @@
     --missed \
     --show-proportion \
     --title "NFD $(cat VERSION.info)" \
+    --ignore-errors inconsistent,inconsistent \
     --output-directory build/lcov \
     build/coverage.info