scripts: check for, and warn about an unset CT_PREFIX_DIR
The user shall provide a directory to install the toolchain into.
If he/she does not, this is an error, and shall be detected properly,
rather than relying on failure down the road.
Thanks to "Pedro I. Sanchez" <psanchez@colcan.ca> for pointing out
the issue:
http://sourceware.org/ml/crossgcc/2009-12/msg00011.html
4 select ARCH_SUPPORTS_32
5 select ARCH_SUPPORTS_64
8 select ARCH_SUPPORT_ARCH
9 select ARCH_SUPPORT_CPU
10 select ARCH_SUPPORT_TUNE
12 The x86 architecture, as defined by:
13 32-bit (ia32) : http://www.intel.com/
14 64-bit (amd64): http://www.amd.com/us-en/Processors/DevelopWithAMD/0,,30_2252_875_7044,00.html