The HLS 2012.3 (UG902) user guide contains an error regarding compiler options in the 2012.3 version of (UG902):
Page 55 of UG902 (V2012.3) states that the apcc compiler option can be enabled in the project by selecting the "Use APCC for compiling C files" option in the project settings (Simulation Settings).
On the next page (pg-56) of the user guide there is a screen capture of this option taken from HLS 2012.2.
However, in Vivado HLS 2012.3 this option is not present in the project settings.
This will be corrected in a future update.
In Vivado HLS 2012.3, the APCC compiler is enabled by default if the project is a C++ project and it includes the header files for arbitrary precision arithmetic.