Allow shared builds of libwebm.

Omit the STATIC in the add_library command, and stop
forcing static MSVC runtimes when BUILD_SHARED_LIBS
is enabled.

$ cmake path/to/libwebm -DBUILD_SHARED_LIBS=1 && cmake --build .

Change-Id: I4935c774d98f70a39363f37be4f9e8989a0749c0
1 file changed