[PHP] New version of upb, and a new hash function wyhash in third_party.

[haberman]

This brings a bunch of upb performance improvements, particularly in descriptor loading. PHP should see a significant improvement in the speed of imports of generated classes.

This includes two sets of optimizations to descriptor loading:

• Optimized the loading of descriptors upb#328 (-39% CPU time)
• symtab: use longjmp() for errors and avoid intermediate table. upb#330 (-31% CPU time)

So overall I anticipate that Ads will see a >2x speedup in the up-front cost of importing protobuf types.

[stouset]

Building from source fails due to not finding wyhash.

$ cat Gemfile | grep google-protobuf
gem 'google-protobuf', git: 'https://github.com/protocolbuffers/protobuf'

$ bundle
…
convert.c:44:10: fatal error: 'third_party/wyhash/wyhash.h' file not found
#include "third_party/wyhash/wyhash.h"
         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2 warnings and 1 error generated.
make: *** [convert.o] Error 1

I'm guessing the appropriate -I flag isn't passed to the compiler, as the third_party directory is in the toplevel of the project, and not available in the ruby subdirectory.

[stouset]

Adding

find_header('third_party/wyhash/wyhash.h', '../../../..')

to extconf.rb appears to resolve this.