PCH documentation (wip)

Help/prop_tgt/PRECOMPILE_HEADERS.rst

+PRECOMPILE_HEADERS
+------------------
+
+List of header files to precompile.
+
+Precompiling header files can speed up compilation by creating a partially
+processed version of some header files, and then using that version during
+compilations rather than repeatedly parsing the original headers.
+List all header files that should be precompiled in the PRECOMPILE_HEADERS
+property.   If precompiled headers are not supported by the platform, this
+property will be ignored.