Add python as a pkg-config dependency The current libsigrokdecode build passes the python CPPFLAGS and LDFLAGS directly into libsigrokdecode.pc.in. This leads to issues while cross-compiling as while using PKG_CONFIG_SYSROOT_DIR, there is a chance of the prefix being duplicated. We now, while detecting the installation of python (cross or normal), add a dependency for the module name in the pkgconfig file (from configure.ac).