Shave off 1.3s of THeader.h compile time

Shave off 1.3s of THeader.h compile time

Summary:
THeader.h went from 1.8s to 0.5s.
Total build of sample project doing thrift client and server stuff went
down 1.5-3% from

```
(run 1)
real    5m25.059s
user    130m30.853s
sys     10m18.642s

(run 2)
real    5m29.483s
user    129m12.209s
sys     10m14.762s
```

to
```
(run 1)
real    5m23.292s
user    125m44.318s
sys     10m7.103s

(run 2)
real    5m20.999s
user    127m4.969s
sys     10m10.118s
```

Test Plan:
fbmake --distcc off --ccache off dbg
Will also watch contbuild, since some files might be missing includes

Reviewed By: haijunz@fb.com

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FB internal diff: D2029911

Signature: t1:2029911:1430261056:9ae688c50585a6454479f810d80b2c1c79b60e04