Unable to compile on Cygwin

I am attempting to compile Clang on Cygwin. I get an error and would appreciate any pointers on how to proceed.

I checked out llvm, clang, clang extra tools, and compiler-rt.

I compiled using:
cmake …/llvm
make

I get the following failure:

[ 57%] Built target gtest_main
[ 57%] Building C object projects/compiler-rt/lib/builtins/CMakeFiles/clang_rt.builtins-x86_64.dir/x86_64/floatdidf.c.o
In file included from /home/DiltsDa/arm/llvm/projects/compiler-rt/lib/builtins/x86_64/…/int_types.h:21:0,
from /home/DiltsDa/arm/llvm/projects/compiler-rt/lib/builtins/x86_64/…/int_lib.h:51,
from /home/DiltsDa/arm/llvm/projects/compiler-rt/lib/builtins/x86_64/floatdidf.c:9:
/home/DiltsDa/arm/llvm/projects/compiler-rt/lib/builtins/x86_64/…/int_endianness.h:109:2: error: #error Unable to determine endian
#error Unable to determine endian
^
projects/compiler-rt/lib/builtins/CMakeFiles/clang_rt.builtins-x86_64.dir/build.make:57: recipe for target ‘projects/compiler-rt/lib/builtins/CMakeFiles/clang_rt.builtins-x86_64.dir/x86_64/floatdidf.c.o’ failed
make[2]: *** [projects/compiler-rt/lib/builtins/CMakeFiles/clang_rt.builtins-x86_64.dir/x86_64/floatdidf.c.o] Error 1
CMakeFiles/Makefile2:7316: recipe for target ‘projects/compiler-rt/lib/builtins/CMakeFiles/clang_rt.builtins-x86_64.dir/all’ failed
make[1]: *** [projects/compiler-rt/lib/builtins/CMakeFiles/clang_rt.builtins-x86_64.dir/all] Error 2
Makefile:136: recipe for target ‘all’ failed
make: *** [all] Error 2