PE/COFF does not permit weak linking semantics. This means that the
expression `&symbol == NULL` is tautologically false. In order to
support this semantic, the symbol needs to be dynamically looked up at
runtime. Since the ObjC runtime is not in use on Windows currently,
just ignore this for the time being. Silences a warning from clang
about the tautological comparison.
Also have swift-reflection-test check if the symbol exists. This allows swift-reflection-test to work with older Remote Mirror dylibs that don't have it.
rdar://problem/50030805
Recent Swift uses 2 as the is-Swift bit when running on newer versions, and 1 on older versions. Since it's difficult or impossible to know what we'll be running on at build time, make the selection at runtime.
If one thinks about it, swift's build has two sections: a runtime or target
section (i.e. ./stdlib) and a host section (everything
else). swift-reflection-test is an abberation from that pattern since it is
built for target platforms but is in the section of host tools.
In this commit, I move it into ./stdlib. Beyond being a bitter location
conceptually this will additionally allow me to avoid a dependency cycle in
between the compiler and the stdlib build.
After this, there is only one more target in the compiler code: swift-lang. From
talking with Xi Ge, we can move that into its own separate project as a
package. Once that is done, I will not have any more cycles.
