x86 doxygen broken.

I am getting the following error:

```
FAILED: api/docs/html/index.html
cd /usr/local/google/home/hgreving/dynamorio/build/api/docs && /usr/bin/cmake -D DOXYGEN_EXECUTABLE=/usr/bin/doxygen -Ddoxygen_ver=1.8.13 -Dversion_number=7.91.18087 "-Dmodule_string_long=\"DynamoRIO Extension Details\"" -Dmodule_string_short=\"Extension\" -Dhome_url=\"http://www.dynamorio.org\" "-Dhome_title=\"DynamoRIO Home Page\"" -Dlogo_imgfile=\"drlogo.png\" -P /usr/local/google/home/hgreving/dynamorio/src/api/docs/CMake_rundoxygen.cmake
CMake Error at /usr/local/google/home/hgreving/dynamorio/src/api/docs/CMake_rundoxygen.cmake:143 (message):
*** /usr/bin/doxygen failed: ***

/usr/local/google/home/hgreving/dynamorio/build/include/dr_ir_instr.h:978:
warning: explicit link request to 'DR_PRED_AL' could not be resolved

/usr/local/google/home/hgreving/dynamorio/build/include/dr_ir_instr.h:978:
warning: explicit link request to 'DR_PRED_OP' could not be resolved

/usr/local/google/home/hgreving/dynamorio/build/include/dr_ir_instr.h:978:
warning: explicit link request to 'DR_PRED_AL' could not be resolved

/usr/local/google/home/hgreving/dynamorio/build/include/dr_ir_instr.h:979:
warning: explicit link request to 'DR_PRED_NV' could not be resolved
```