To test a compiler's performances, you use it to compile stuff don't you? That's what TFA does: it builds GCC 4.7 using both a C compiler and a C++ compiler, then looks how the results perform, by compiling stuff with them.
TFA did not bench how long the original compilation (whether through C or through C++) took, that would have been pointless and irrelevant.
Comments
To test a compiler's performances, you use it to compile stuff don't you? That's what TFA does: it builds GCC 4.7 using both a C compiler and a C++ compiler, then looks how the results perform, by compiling stuff with them.
TFA did not bench how long the original compilation (whether through C or through C++) took, that would have been pointless and irrelevant.