Do not set CPPFLAGS, CXXFLAGS, and LDFLAGS in configure

[Peter Johansson]

Setting CPPFLAGS, CXXFLAGS, and LDFLAGS in configure is bad style.

See for example ​Automake manual 27.6.1 in which they suggest:

You should not add options to these user variables within configure either, for the same reason. Occasionally you need to modify these variables to perform a test, but you should reset their values afterwards. In contrast, it is OK to modify the ‘AM_’ variables within configure if you AC_SUBST them, but it is rather rare that you need to do this, unless you really want to change the default definitions of the ‘AM_’ variables in all Makefiles.

I suggest the following structure (I use CPPFLAGS here as an example; the same structure could be used for other flags as well):

1. Save flag given by user - CPPFLAGS_SAVE = CPPFLAGS
2. Set SD_CPPFLAGS depending on --enable-debug, --with-apr, and --with-svn
3. Set CPPFLAGS = SD_CPPFLAGS CPPFLAGS
4. Perform tests
5. export SD_CPPFLAGS using AC_SUBST
6. reset CPPFLAGS to CPPFLAGS_SAVE
7. AC_OUTPUT

The major change is that we need to split up chunks such as APR stuff, because some part belong in 2) and some parts belong in 4).

[Peter Johansson]

fixed in [640]