Use IMPALA_COMPRESSED_DEBUG_INFO=true by default

A large part of the Impala binary's size is debug information. The IMPALA_COMPRESSED_DEBUG_INFO environment variable was introduced in IMPALA-11511 and reduces the binary size by >50%. For developer environments, this is can dramatically reduce disk space usage, especially when building the backend tests. The downside is slower linking and slower processing of the debuginfo (attaching with GDB, dumping symbols for minidumps).

The disk space difference is very large, and this can help enable us to expand debug information for the toolchain. We should switch the default value to true.