[clang] [clang] Only build static analyzer sources if requested (PR #71653)

[via cfe-commits]

whisperity wrote:

Took some measurements on X86. Size-wise the CSA-related libraries and objects are roughly the same. We have 2.2G for the three libraries `lib/libclangStaticAnalzyer{Checkers,Core,Frontend}.a` and then another 2.2G for the `tools/clang/lib/StaticAnalyzer/**` object files. The sizes are a LOT different on X86, however, as the build directory is close to 90 GiB, so now CSA only accounts for "just" 5.5%.

Here, I got 201 build actions to (re-)execute with a raw `ninja` to generate these files as opposed to `ninja clang`, and with `-j 16` and 64 GiB RAM available, the execution of these ~200 commands took 4 min 47 seconds to execute, which is ~9.8% of the total build time otherwise (42 min).

https://github.com/llvm/llvm-project/pull/71653