[scudo] Make the placeholder type specifier be consistent with C/C++

This avoids `-Wformat` complains the placeholder type specifier mismatch
on `lld`/`llu`(used for `s64`/`u64`) which have slightly different
interpretation in string_utils.cpp.

Also enable Timer build which was disabled because of the complaining of
`-Wformat`.

Differential Revision: https://reviews.llvm.org/D147496