LLVM is described as 'Compiler infrastructure designed for compile-time, link-time, run-time, and "idle-time" optimization of programs written in arbitrary programming languages. Originally implemented for C and C++, the language-agnostic design (and the success) of LLVM has since' and is a Compiler in the development category. There are seven alternatives to LLVM for a variety of platforms, including Linux, Windows, Mac, BSD and Cygwin apps. The best LLVM alternative is MinGW, which is both free and Open Source. Other great apps like LLVM are GNU Compiler Collection, clang, Tiny C Compiler and QBE.
LLVM is not a C compiler. Clang is a C compiler that uses LLVM