New gpg-error-config can parse (simpler) *.pc file. It can be used for other software.
For the use cases of *-config command, new gpg-error-config can be used, directly, or indirectly.
- libassuan-config can call gpg-error-config, having libassuan.pc
- Or, libassuan.m4 can be modified using gpg-error-config, instead of libassuan-config
- For libksba, libgcrypt and libassuan
- update its use of gpg-error.m4 from master
- provide *.pc
- fix *-config to be compatible to pkg-config way
- modify *.m4 to use gpg-error-config
- [optionally?] modify *-config to wrap gpg-error-config
- Test with ntbtls, which uses libksba, libgcrypt, and libgpg-error
- ntbtls also provides ntbtls.pc
- modify ntbtls.m4
- [optionally] we can remove *-config scripts and only have gpg-error-config
- npth doesn't depend on libgpg-error (this situation is different to other software)
- providing npth.pc is good
- use of gpg-error-config in npth.m4 is considered OK
- GnuPG build keeps no other dependency of pkg-config
- Developers of application can use *.m4 (no use of pkg-config) or PKG_CHECK_MODULES in pkg.m4.
- In major use case(s), we won't need --with-*-prefix option to configure software