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).