pjproject: bump to 2.12.1

pjproject: bump to 2.12.1

- add "--disable-android-mediacodec" to configure
- add EXCLUDE_APP=1 to "make" calls so some apps aren't built (speeds up
  the build a bit)
- drop "sed" call as no longer needed
- drop uclibc related patches
  (0002-uclibc-linker-unrecognized-options.patch and
  0003-non-gnu-pthreads.patch)
- update 0004-config_site.patch to sync up with Asterisk 18.14.0
- drop 0005-remove-hardcoded-lstdc++.patch as uclibcxx was removed from
  OpenWrt
- update 0006-fix-pkg_config-file.patch as there were some changes in
  this area upstream
- add 0007-execinfo.patch to prevent errors due to missing <execinfo.h>
- sync patches with 18.14.0

Signed-off-by: Sebastian Kemper <sebastian_ml@gmx.net>