fixdep: do not ignore kconfig.h

kconfig.h was excluded from consideration by fixdep by 6a5be57f0f00 (fixdep: fix extraneous dependencies) to avoid some false positive hits (1) include/config/.h (2) include/config/h.h (3) include/config/foo.h (1) occurred because kconfig.h contains the string CONFIG_ in a comment. However, since dee81e988674 (fixdep: faster CONFIG_ search), we have a check that the part after CONFIG_ is non-empty, so this does not happen anymore (and CONFIG_ appears by itself elsewhere, so that check is worthwhile). (2) comes from the include guard, __LINUX_KCONFIG_H. But with the previous patch, we no longer match that either. That leaves (3), which amounts to one [1] false dependency (aka stat() call done by make), which I think we can live with: We've already had one case [2] where the lack of include/linux/kconfig.h in the .o.cmd file caused a missing rebuild, and while I originally thought we should just put kconfig.h in the dependency list without parsing it for the CONFIG_ pattern, we actually do have some real CONFIG_ symbols mentioned in it, and one can imagine some translation unit that just does '#ifdef __BIG_ENDIAN' but doesn't through some other header actually depend on CONFIG_CPU_BIG_ENDIAN - so changing the target endianness could end up rebuilding the world, minus that small TU. Quoting Linus, ... when missing dependencies cause a missed re-compile, the resulting bugs can be _really_ subtle. [1] well, two, we now also have CONFIG_BOOGER/booger.h - we could change that to FOO if we care [2] https://lkml.org/lkml/2018/2/22/838

RVRasmus Villemoes committed 8 years ago