Improve Python's handling of CFLAGS and friends

http://bugs.python.org/issue9189

`../src/configure --with-pydebug && make` originally produced

  gcc -c -fno-strict-aliasing -g -O2 -g -O0 -Wall -Wstrict-prototypes  -I. -IInclude -I../src/Include   -DPy_BUILD_CORE -o Python/pythonrun.o ../src/Python/pythonrun.c

After this patch, that becomes

  gcc -c -fno-strict-aliasing -g -O0 -Wall -Wstrict-prototypes    -I. -IInclude -I../src/Include    -DPy_BUILD_CORE -o Python/pythonrun.o ../src/Python/pythonrun.c

For `../src/configure --with-pydebug CFLAGS=-g3 && make CFLAGS=-Werror`, we get

  gcc -c -fno-strict-aliasing -g -O0 -Wall -Wstrict-prototypes -g3   -I. -IInclude -I../src/Include    -DPy_BUILD_CORE -o Python/pythonrun.o ../src/Python/pythonrun.c

Without pydebug, we get:

  gcc -c -fno-strict-aliasing -DNDEBUG -g -fwrapv -O3 -Wall -Wstrict-prototypes    -I. -IInclude -I../src/Include    -DPy_BUILD_CORE -o Python/pythonrun.o ../src/Python/pythonrun.c

[brett.cannon, 2010-07-07 04:07:22]

LGTM short of one letter change in the NEWS entry.

http://codereview.appspot.com/1749042/diff/2001/3003
File Misc/NEWS (right):

http://codereview.appspot.com/1749042/diff/2001/3003#newcode1513
Misc/NEWS:1513: - Made a user-specified CFLAGS, CPPFLAGS, or LDFLAGS setting
override
"Made" -> "Make"

[Antoine Pitrou, 2010-07-09 00:16:12]

http://codereview.appspot.com/1749042/diff/9001/10004
File Lib/sysconfig.py (right):

http://codereview.appspot.com/1749042/diff/9001/10004#newcode265
Lib/sysconfig.py:265: done[var] = done['PY_' + var]
Why do you need to do that?

Right now, you have:

>>> sysconfig.get_config_var('CFLAGS')
'-g -O2 -DNDEBUG -g -fwrapv -O3 -Wall -Wstrict-prototypes'
>>> sysconfig.get_config_var('PY_CFLAGS')
'-g -O2 -DNDEBUG -g -fwrapv -O3 -Wall -Wstrict-prototypes -I. -IInclude
-I./Include  -DPy_BUILD_CORE'

[Jeffrey Yasskin, 2010-07-09 00:55:48]

http://codereview.appspot.com/1749042/diff/9001/10004
File Lib/sysconfig.py (right):

http://codereview.appspot.com/1749042/diff/9001/10004#newcode265
Lib/sysconfig.py:265: done[var] = done['PY_' + var]
On 2010/07/09 00:16:13, Antoine Pitrou wrote:
> Why do you need to do that?
> 
> Right now, you have:
> 
> >>> sysconfig.get_config_var('CFLAGS')
> '-g -O2 -DNDEBUG -g -fwrapv -O3 -Wall -Wstrict-prototypes'
> >>> sysconfig.get_config_var('PY_CFLAGS')
> '-g -O2 -DNDEBUG -g -fwrapv -O3 -Wall -Wstrict-prototypes -I. -IInclude
> -I./Include  -DPy_BUILD_CORE'

The above is the behavior in SVN. Well, I get:
>>> sysconfig.get_config_var('CFLAGS')
'-fno-strict-aliasing -g -O2 -DNDEBUG -g -fwrapv -O3 -Wall -Wstrict-prototypes'
>>> sysconfig.get_config_var('PY_CFLAGS')
'-fno-strict-aliasing -g -O2 -DNDEBUG -g -fwrapv -O3 -Wall -Wstrict-prototypes
-I. -IInclude -I../src/Include  -DPy_BUILD_CORE'
>>> sysconfig.get_config_var('PY_CORE_CFLAGS')
>>> 

After the patch, I get:
>>> sysconfig.get_config_var('CFLAGS')
'-fno-strict-aliasing -DNDEBUG -g -fwrapv -O3 -Wall -Wstrict-prototypes'
>>> sysconfig.get_config_var('PY_CFLAGS')
'-fno-strict-aliasing -DNDEBUG -g -fwrapv -O3 -Wall -Wstrict-prototypes'
>>> sysconfig.get_config_var('PY_CORE_CFLAGS')
'-fno-strict-aliasing -DNDEBUG -g -fwrapv -O3 -Wall -Wstrict-prototypes -I.
-IInclude -I../src/Include  -DPy_BUILD_CORE'

Note that after this patch, CFLAGS isn't assigned in the Makefile, so it would
have an empty value, were it not for the above lines.
Parts of distutils assume that 'CFLAGS' will have the above value. So I kept
backward-compatibility by assigning the new values back to the old names.
Distutils doesn't seem to look for the old value of 'PY_CFLAGS' (which I renamed
to PY_CORE_CFLAGS at Marc-Andre's request). That's logical, since distutils
doesn't want to define Py_BUILD_CORE.