scons: Add warning for missing declarations

This patch enables warnings for missing declarations. To avoid issues
with SWIG-generated code, the warning is only applied to non-SWIG
code.

MAC: Make gem5 compile and run on MacOSX 10.7.2

Adaptations to make gem5 compile and run on OSX 10.7.2, with a stock
gcc 4.2.1 and the remaining dependencies from macports, i.e. python
2.7,.2 swig 2.0.4, mercurial 2.0. The changes include an adaptation of
the SConstruct to handle non-library linker flags, and Darwin-specific
code to find the memory usage of gem5. A number of Ruby files relied
on ambigious uint (without the 32 suffix) which caused compilation
errors.

types: Move stuff for global types into src/base/types.hh

String constant const-ness changes to placate g++ 4.2.
Also some bug fixes in MIPS ISA uncovered by g++ warnings
(Python string compares don't work in C++!).

Updated Authors from bk prs info

New directory structure:
- simulator source now in 'src' subdirectory
- imported files from 'ext' repository
- support building in arbitrary places, including
outside of the source tree. See comment at top
of SConstruct file for more details.
Regression tests are temporarily disabled; that
syetem needs more extensive revisions.

SConstruct:
Update for new directory structure.
Modify to support build trees that are not subdirectories
of the source tree. See comment at top of file for
more details.
Regression tests are temporarily disabled.
src/arch/SConscript:
src/arch/isa_parser.py:
src/python/SConscript:
Update for new directory structure.