Problem installing last build of Sniffles
You need to install GCC, or a newer version of Clang.

Your compiler — though the binary is called gcc — is actually Clang, and the Clang version that’s shipping with macOS/Xcode still does not support OpenMP.

The easiest course of action is probably to install GCC via Homebrew (brew install gcc) and then configure Sniffles to use Homebrew’s GCC (i.e. setting the CMAKE_C*_COMPILER paths to /usr/local/bin/g{cc,++}-$version).