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
diff --git a/runtime/jit/jit.h b/runtime/jit/jit.h
index 2ddcd2d..8c1b688 100644
--- a/runtime/jit/jit.h
+++ b/runtime/jit/jit.h
@@ -194,7 +194,7 @@
       REQUIRES_SHARED(Locks::mutator_lock_) = 0;
   virtual bool GenerateDebugInfo() = 0;
   virtual void ParseCompilerOptions() = 0;
-  virtual bool IsBaselineCompiler() const;
+  virtual bool IsBaselineCompiler() const = 0;
 
   virtual std::vector<uint8_t> PackElfFileForJIT(ArrayRef<const JITCodeEntry*> elf_files,
                                                  ArrayRef<const void*> removed_symbols,