Missing condition on CAPSTONE_BUILD_CORE_ONLY in Makefile

[Summus-31c04089c3cd80]

Hello,

I wanted to build capstone with CAPSTONE_BUILD_CORE_ONLY=yes because I don't need cstool and the others things.
The build is correct, not building cstool, but the install (and others rules) don't check about CAPSTONE_BUILD_CORE_ONLY before trying to use / delete cstool binary.

So, when I do
make CAPSTONE_BUILD_CORE_ONLY=yes
and then
make install CAPSTONE_BUILD_CORE_ONLY=yes
I get and error because cstool/cstool doesn't exist.

I'm doing a pull request to fix it.