[CMake] namespace support

[Peter Kümmel]

I wanna build several targets in one CMakeLists.txt,
because I have many simple one-file-only plugins with
the same build rules, for instance:

include_directories(a)
add_library(a MODULE a/a.cpp)

include_directories(b)
add_library(b MODULE b/b.cpp)



The problem is that all include_directories and
add_definitions have a file scope and are visible
for all targets.

Is it already possible to use push/pop the scope like it
must be done for add_subdirectory?

scope_push()
	include_directories(a)
	add_library(a MODULE a/a.cpp)
scope_pop()

or

scope_enter(b)
	include_directories(b)
	add_library(b MODULE b/b.cpp)
scope_leave()

or

namespace(a)
	include_directories(a)
	add_library(a MODULE a/a.cpp)
endnamespace()


Peter