cmake: fix building statically by Ninja

An attempt to build Tarantool statically by Ninja (with the
enabled CMake option BUILD_STATIC_WITH_BUNDLED_LIBS), error below
is produced:

 | ninja: error: build.ninja:1405: bad $-escape
 | (literal $ must be written as $$)

The commit fixes that error. Follows up commit c92a1699
("cmake: support build using Ninja").

NO_CHANGELOG=build
NO_DOC=build
NO_TEST=build

(cherry picked from commit d48c40e69495b8cc3475ea0b184768054d87b780)