can't change variable value

[Mikhail Kruk]

Hi,
I want to run my make like this:
make BUILDTYPE=release
to build release version and any other invokation of make should build 
debug version. 

So I have the following code in makefile:

ifneq ($(BUILDTYPE), release)
        export BUILDTYPE = debug
        CC = cc -g
else
        CC = cc -O3
endif
...

This works for 'make BUILDTYPE=release'
this also works for 'make' (BUILDTYPE gets assigned 'debug' value)
However if I run it like 'make BUILDTYPE=blah' BUILDTYPE will preserve the 
value 'blah'. 
Recursive invokation of make is done, so I suspect this might be at fault.

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