Previously each object was effectively compiled twice: once with
-showIncludes -Zs just for the dependencies, and once for real. Pass
-showIncludes on the actual compilation instead and let the mscl helper
convert the include records into the .d file.
make -j32 with MSVC 2026:
before:
1:40.35 elapsed, 345 s user+sys
after:
0:59.86 elapsed, 124 s user+sys
no .d generation:
0:59.66 elapsed, 129 s user+sys
making dependency generation nearly free.
Signed-off-by: Kacper Michajłow <kasper93@gmail.com>
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