Put -D and -I flags into CPPFLAGS rather than into CFLAGS; that should

Put -D and -I flags into CPPFLAGS rather than into CFLAGS; that should
make them apply to C++ as well as C.  That seems to be what the autoconf
documentation suggests:

- Variable: CFLAGS
  Debugging and optimization options for the C compiler. If it is not set
  in the environment when configure runs, the default value is set when
  you call AC_PROG_CC (or empty if you don't). configure uses this
  variable when compiling or linking programs to test for C features.

  If a compiler option affects only the behavior of the preprocessor
  (e.g., -Dname), it should be put into CPPFLAGS instead. If it affects
  only the linker (e.g., -Ldirectory), it should be put into LDFLAGS
  instead. If it affects only the compiler proper, CFLAGS is the natural
  home for it. If an option affects multiple phases of the compiler,
  though, matters get tricky. One approach to put such options directly
  into CC, e.g., CC='gcc -m64'. Another is to put them into both CPPFLAGS
  and LDFLAGS, but not into CFLAGS.

	...

- Variable: CPPFLAGS
  Preprocessor options for the C, C++, Objective C, and Objective C++
  preprocessors and compilers. If it is not set in the environment when
  configure runs, the default value is empty. configure uses this variable
  when preprocessing or compiling programs to test for C, C++, Objective
  C, and Objective C++ features.

  This variable's contents should contain options like -I, -D, and -U that
  affect only the behavior of the preprocessor. Please see the explanation
  of CFLAGS for what you can do if an option affects other phases of the
  compiler as well.

git-svn-id: http://anonsvn.wireshark.org/wireshark/trunk@41593 f5534014-38df-0310-8fa8-9805f1628bb7