Irony server fails to install using an up-to-date version of Homebrew with LLVM installed

[goxberry]

Irony server fails to install on macOS 10.14.5 with current Homebrew (as of the time this issue was filed) and LLVM 8 installed via Homebrew. The source of the error, as far as I can tell, is that the current version of LLVM 8 in Homebrew is 8.0.0_1 instead of 8.0.0 -- this sort of "underscored version" tends to occur when a package needs to be updated due to updates in dependency package versions.