Add support for setting CPPFLAGS and LDFLAGS

[swt2c]

No description provided.

[TobiasFaller]

What is the purpose of the CPPFLAGS variable? (Typically it is used for the C Pre-Processor)

What is the use of Cppflags?
CPPFLAGS is used to pass extra flags to the C preprocessor. These flags are also used by any programs that use the C preprocessor, including the C, C++, and Fortran compilers. You do not need to explicitly call the C preprocessor.

It seems that it contains additional flags for the C++ compiler which could be added to CXXFLAGS instead.
In case additional flags are required for the C compilation I suggest using CFLAGS instead.

[swt2c]

What is the purpose of the CPPFLAGS variable? (Typically it is used for the C Pre-Processor)

What is the use of Cppflags?
CPPFLAGS is used to pass extra flags to the C preprocessor. These flags are also used by any programs that use the C preprocessor, including the C, C++, and Fortran compilers. You do not need to explicitly call the C preprocessor.

Well, as you noted the C preprocessor is used by C++ compilers also. In my particular case (Debian packaging), these flags are being set by the build environment, so I'd rather not have to change them.

[arminbiere]

For external input, we have the policy to have the commits signed:

See CONTRIBUTING.md.

[swt2c]

For external input, we have the policy to have the commits signed:

See CONTRIBUTING.md.

Done (and rebased).

[arminbiere]

In another context it was mentioned that those flags handed to configure should not be changed and used as is for compilation. We first need to research that before we change the way how this is done.