Fix linker error in JitCompilerInterface.

This patch fixed linker "undefined symbol" issue:
JitCompilerInterface is an interface class and doesn't provide
implementations; making the virtual function IsBaselineCompiler
pure fixes the linker issue present for O0 build.

Test: test-art-target, test-art-host.
Change-Id: Id0f4ad1a605631f89f9fdd340e70d4af61e465aa
1 file changed