The Arduino compiler is a GNU C++ compiler HOWEVER there is no c runtime library (which is not part of the compiler).
Probably more significant to the question is that the Arduino compiler supplies support for the ATMEL hardware. This is incompatible with the Raspberry Pi.
The Arduino is a real time microcontroller and has unrestricted access to its hardware, the Pi usually runs a multi-tasking OS, the hardware is not directly accessible from user space, so many tasks need to be written differently; often this means relying on a OS supplied kernel driver.
Any practicable Arduino program would require extensive changes to work on the Raspberry Pi. The effort involved is likely to be more than writing a Raspberry Pi program from scratch.