The file hw/xfree86/common/xf86Build.h is generated by configure, which means it shouldn't be included in the distributed tarballs. However, in hw/xfree86/common/Makefile.am it is listed in libinit_a_SOURCES, which ends up in DIST_SOURCES in the Makefile. It looks like xf86Build.h should be in nodist_libinit_a_SOURCES instead.
Sorry about the phenomenal bug spam, guys. Adding xorg-team@ to the QA contact so bugs don't get lost in future.
fixed in 35346a42271dfe65fe0a86dc522701028bf6daf6.
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