[CMake] lexical scoping

[Bill Hoffman]

I have an idea.  What if we created a variable_scope command?

Something like this:

set(a "world")
variable_scope_begin(a)
set(a "hello")
message(${a})
variable_scope_end(a)
message(${a})


The above would print out:
hello
world

This could be done with the current macros, or even an include file of 
cmake without having to create the idea of a function.  You could of 
course pass in a list of variables to variable_scope. It would be sort 
of like the "my" in perl.   I don't think it would be that hard to 
implement this, and it would be backwards compatible, and not make the 
set command any more complicated.  You could nest them as well.  It 
could cause some odd things to happen if you forgot to add the 
scope_end, but it might fix more things than it breaks.

-Bill