Tests/ObjectLibrary: Do not enable CXX in subdirectories

In commit b237dbd8 (Xcode: Fix object library references in
multi-project trees, 2012-08-03) we accidentally enabled CXX in the
subdiretories of this test by invoking project() with only one argument.
The top-level directory of the test enables only C, so do this in the
subdirectories too.

Tests/ObjectLibrary/A/CMakeLists.txt

@@ -1,4 +1,4 @@
-project(ObjectLibraryA)
+project(ObjectLibraryA C)
 # Add -fPIC so objects can be used in shared libraries.
 # TODO: Need property for this.
 if(CMAKE_SHARED_LIBRARY_C_FLAGS AND NOT WATCOM)

Tests/ObjectLibrary/B/CMakeLists.txt

@@ -1,4 +1,4 @@
-project(ObjectLibraryB)
+project(ObjectLibraryB C)
 if("${CMAKE_GENERATOR}" MATCHES "Visual Studio 6")
   # VS 6 generator does not use per-target object locations.
   set(vs6 _vs6)