Compiler:
A working C99 compiler or better, such as gcc-4.x or clang-3.4.
This notation specifies a minimum required package version (-ver) or an exact version (=ver). For example, bison=2.x requires the 2.x branch of bison, not 3.x.
C: As a minimum, a compiler supporting the C90. Pretty much any modern C compiler will do, but gcc or clang is recommended. Note that MSVC++ is not a C compiler.
C++: A C++11 compliant compiler is recommended.