libsolv_build: declare missing dependency
BSolver: fix build host build for gcc 2

gcc 2 doesn't support the weakref attribute. Rather use the regular
(target) method to initialize sCreateSolver instead (pthread once,
dlopen()). Since we know that we're on Haiku, that doesn't add any
dependencies that aren't available anyway.
libsolv_build: fix build on gcc 2 Haiku

* Fix the "UseHeaders" invocation for libsolvext to use the correct
  directory.
* Reorder things slightly, merely for aesthetical reasons.
Update packages binutils, gcc, add missing bepdf source package