Add type_traits include to logging.cc (#18)

This fixes an error about std::aligned_storage not found when built with
clang22.

Enforce the use of stacktrace_generic-inl.h across all platforms (#17)

Also add a .gitignore.

Ensure we use the backtrace function regardless of the OS (#16)

A follow-up for e06a7bb. We should be using the backtrace function on macOS as well, not only on Linux.

Use glibc-provided backtrace function to unwind the stack on Linux (#15)

Ensure that we always use the glibc-provided backtrace function on Linux to unwind the stack. This function proved to be the most stable in our tests (see debug-util-test.cc in yugabyte-db sources). Also implement protection from double entry into the backtrace function similar to what was implemented in yugabyte/yugabyte-db@3e34805. Finally, enhance stacktrace_unittest so that it provides detailed information in case of an error, e.g. if the actual stack trace is shifted relative to the expected result.

Add an optional prefix message to every log message (#12)

* SetLogPrefix

Add an optional prefix message to every log message (#12)

* SetLogPrefix

Add UTC timestamp to top of each log file. (#11)

This change adds a log for the current UTC at the top of each log file, which should make it easier to determine what timezone the logs are using.

Example:
```
Log file created at: 2022/09/15 19:29:13
Current UTC time: 2022/09/15 23:29:13
```

Allow updating vmodule levels after vmodule was parsed, invalidate al…

…ready cached site flags

Removed email sending functionality (#7)

This removes email sending functionality as per yugabyte/yugabyte-db#11930.

The relevant gflags remain in place to avoid any issues with clusters that already have the flags set, but no longer do anything.

(The previous pull request #6 was merged into the master-yb branch, but as of 05/25/2022 we are using the 0.4.0-yb branch, which is the target branch of this pull request.)

Merge pull request google#812 from google/release-0.6

release 0.6