Why does export CC=/usr/bin/gcc not change the environment variable

Question

I'm using a bash shell in Cygwin. CC is set to a mingw compiler.

$ env | grep CC
CC=x86_64-w64-mingw32-gcc.exe

I want to change it to /usr/bin/gcc.

$ export CC=/usr/bin/gcc
$ env | grep CC
CC=x86_64-w64-mingw32-gcc.exe

I noticed that in my ~/.bashrc file there is a line

set CC=x86_64-w64-mingw32-gcc.exe

But even when I change that line to /usr/bin/gcc, CC is still set to the mingw compiler.