docs build error with doxygen 1.7.4

_From [bruen...@google.com](https://code.google.com/u/109494838902877177630/) on April 15, 2014 14:05:42_

This is likely the first time I've built in my win8x64 VM since we added
these drcov and drltrace docs pages. They don't build:

FAILED: cmd.exe /c cd C:\derek\dr\git\build_x86_dbg_tests\api\docs && C:\PROGRA~2\CMake2~1.8\bin\cmake.exe -D DOXYGEN_EXECUTABLE=C:/cygwin/bin/doxygen.exe -Ddoxygen_ver=1.7.4 -Dversion_number=4.2.2669 "-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 C:/derek/dr/git/src/api/docs/CMake_rundoxygen.cmake
CMake Error at C:/derek/dr/git/src/api/docs/CMake_rundoxygen.cmake:143 (message):
**\* C:/cygwin/bin/doxygen.exe failed: ***

/c/derek/dr/git/src/api/docs/release.dox:149: warning: unable to resolve
reference to `page_drltrace' for \ref command

/c/derek/dr/git/src/api/docs/release.dox:150: warning: unable to resolve
reference to `page_drcov' for \ref command

/c/derek/dr/git/build_x86_dbg_tests/api/docs/tool_gendox.dox:46: warning:
unable to resolve reference to `page_drcov' for \ref command

/c/derek/dr/git/build_x86_dbg_tests/api/docs/tool_gendox.dox:47: warning:
unable to resolve reference to `page_drltrace' for \ref command

Doxyfile has:

INPUT = "/c/derek/dr/git/src/api/docs" \
"/c/derek/dr/git/build_x86_dbg_tests/include" \
"/c/derek/dr/git/build_x86_dbg_tests/api/docs" \
"/c/derek/dr/git/src/ext/drcontainers" \
"/c/derek/dr/git/src/ext/drgui" \
"/c/derek/dr/git/src/ext/drmgr" \
"/c/derek/dr/git/src/ext/drsyms" \
"/c/derek/dr/git/src/ext/drutil" \
"/c/derek/dr/git/src/ext/drwrap" \
"/c/derek/dr/git/src/ext/drx"

FILE_PATTERNS = *.h \
*.dox

% grep page_drltrace api/docs/*.dox
api/docs/tool_gendox.dox:- \subpage page_drltrace

% doxygen --version
1.7.4

This may be specific to that doxygen version?

_Original issue: http://code.google.com/p/dynamorio/issues/detail?id=1430_