* Follow-up to removed restriction of pch naming on GCC
* Fix pch path conflict on GCC
gcc-pch-generator rewrites target name to a value derived from a header name
and this cases path conflict if multiple pch are created from the same header.
hello.cpp is duplicated in the test for the same reason but for `exe` target --
`exe hello-afx : hello.cpp ;` uses `hello.o` for object file name.
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