ART: Add support for runtime debug checks

Add support for runtime-switchable debug flags. These flags are only
enabled in debug mode, and a constexpr false in release mode. This
allows to distinguish fast from slow checks, for example.

To simplify usage, two macros should be used. DECLARE_RUNTIME_DEBUG_FLAG
defines a static class member or constexpr as the flag. DEFINE_RUNTIME_DEBUG_FLAG
defines the static storage and registers it, if needed. See the
documentation in logging.h.

As is, runtime checks are disabled by default. Pass -XX:SlowDebug=true
to enable them on startup.

Add logging_test. Fix up tests and scripts to enable slow debug checks.

Bug: 35644369
Test: m test-art-host
Change-Id: Icc1cb0bb921d863514c55abef794c5c96f8af801
diff --git a/tools/run-libcore-tests.sh b/tools/run-libcore-tests.sh
index 8b3df3a..6dcc23a 100755
--- a/tools/run-libcore-tests.sh
+++ b/tools/run-libcore-tests.sh
@@ -127,7 +127,7 @@
   elif [[ "$1" == "--debug" ]]; then
     # Remove the --debug from the arguments.
     vogar_args=${vogar_args/$1}
-    vogar_args="$vogar_args --vm-arg -XXlib:libartd.so"
+    vogar_args="$vogar_args --vm-arg -XXlib:libartd.so --vm-arg -XX:SlowDebug=true"
     debug=true
     shift
   elif [[ "$1" == "-Xgc:gcstress" ]]; then