Tests: Teach RunCMake.export to enable languages only when needed

Tests/RunCMake/export/AppendExport-stderr.txt

@@ -1,4 +1,4 @@
-CMake Error at AppendExport.cmake:8 \(export\):
+CMake Error at AppendExport.cmake:[0-9]+ \(export\):
   export EXPORT signature does not recognise the APPEND option.
 Call Stack \(most recent call first\):
   CMakeLists.txt:3 \(include\)

Tests/RunCMake/export/AppendExport.cmake

@@ -1,3 +1,4 @@
+enable_language(CXX)
 add_library(foo empty.cpp)
 export(TARGETS foo FILE "${CMAKE_CURRENT_BINARY_DIR}/foo.cmake")
 install(TARGETS foo EXPORT fooExport

Tests/RunCMake/export/CMakeLists.txt

@@ -1,3 +1,3 @@
 cmake_minimum_required(VERSION 2.8.4)
-project(${RunCMake_TEST})
+project(${RunCMake_TEST} NONE)
 include(${RunCMake_TEST}.cmake)

Tests/RunCMake/export/OldIface-stderr.txt

@@ -1,4 +1,4 @@
-CMake Error at OldIface.cmake:8 \(export\):
+CMake Error at OldIface.cmake:[0-9]+ \(export\):
   export EXPORT signature does not recognise the
   EXPORT_LINK_INTERFACE_LIBRARIES option.
 Call Stack \(most recent call first\):

Tests/RunCMake/export/OldIface.cmake

@@ -1,3 +1,4 @@
+enable_language(CXX)
 add_library(foo empty.cpp)
 export(TARGETS foo FILE "${CMAKE_CURRENT_BINARY_DIR}/foo.cmake")
 install(TARGETS foo EXPORT fooExport