Fix `scalar diagnose` failures (#543)

This resolves #541.

The root cause here is that this loop that intended to get all files
from the `info` directory of the shared object cache _never worked_, but
previously we did not propagate that to a complete failure.

The reason it didn't work is that we tried to read file contents from
the directory path.

I also noticed a silly retry issue because we are now using `run_git()`
which does three retries due to concurrency issues in the functional
tests. We don't want to repeat failures three times in `scalar
diagnose`.

Makefile

@@ -1351,6 +1351,7 @@ BASIC_CFLAGS += -DSHA1DC_FORCE_ALIGNED_ACCESS
 endif
 ifneq ($(filter leak,$(SANITIZERS)),)
 BASIC_CFLAGS += -DSUPPRESS_ANNOTATED_LEAKS
+BASIC_CFLAGS += -O0
 SANITIZE_LEAK = YesCompiledWithIt
 endif
 ifneq ($(filter address,$(SANITIZERS)),)