GCC parses your system header files and produces a modified subset which it uses for compiling. This behaviour ties GCC tightly to the version of your operating system. So, for example, if you were running IRIX 5.3 when you built GCC and then upgrade to IRIX 6.2 later, you will have to rebuild GCC. Similarly for Solaris 2.4, 2.5, or 2.5.1 when you upgrade to 2.6. Sometimes you can type "gcc -v" and it will tell you the version of the operating system it was built against.
If you fail to do this, then it is very likely that Apache will fail to build. One of the most common errors is with
uio.h. This is not a bug with Apache. You will need to re-install GCC.