[grpc] Mark as not supporting static building yet

ports/grpc/portfile.cmake

@@ -1,3 +1,7 @@
+include(${CMAKE_TRIPLET_FILE})
+if (VCPKG_LIBRARY_LINKAGE STREQUAL static)
+    message(FATAL_ERROR "Static building not supported yet")
+endif()
 include(vcpkg_common_functions)
 find_program(GIT git)