[lldb][test] Don't print LLDB version in every test (#201307)
An empty minimal API test currently runs for 330ms on my macOS system.
Of these 330ms, we spend 70ms (20%) just to print the lldb version
number at the start of each test.
This patch disables this behavior by default and instead prints the LLDB
version number once at the start of the LIT test suite. This saves about
2 minutes of CPU time in an LLDB test suite run.