[Cygwin] CYGWIN is not WIN32 in current CMake

[kikairoya]

On old CMake, Cygwin were also WIN32 but currently not. LLVM_ON_UNIX=1 and LLVM_HAVE_LINK_VERSION_SCRIPT=0 should be defined for Cygwin target.

[jeremyd2019]

LGTM

[llvm-ci]

LLVM Buildbot has detected a new failure on builder clang-aarch64-sve2-vla running on linaro-g4-01 while building llvm at step 7 "ninja check 1".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/198/builds/5264

Here is the relevant piece of the build log for the reference

Step 7 (ninja check 1) failure: 1200 seconds without output running [b'ninja', b'check-all'], attempting to kill
...
PASS: lld :: wasm/lto/thinlto.ll (97600 of 97610)
PASS: lld :: wasm/whole-archive.test (97601 of 97610)
PASS: lld :: MachO/stabs.s (97602 of 97610)
PASS: lld :: wasm/unresolved-symbols.s (97603 of 97610)
PASS: lld :: wasm/why-extract.s (97604 of 97610)
PASS: lld :: wasm/libsearch.s (97605 of 97610)
PASS: lld :: MachO/weak-definition-direct-fetch.s (97606 of 97610)
PASS: mlgo-utils :: corpus/extract_ir_test.py (97607 of 97610)
PASS: libFuzzer-aarch64-default-Linux :: value-profile-load.test (97608 of 97610)
PASS: lld :: MinGW/driver.test (97609 of 97610)
command timed out: 1200 seconds without output running [b'ninja', b'check-all'], attempting to kill
process killed by signal 9
program finished with exit code -1
elapsedTime=1539.382116

[llvm-ci]

LLVM Buildbot has detected a new failure on builder ppc64le-flang-rhel-clang running on ppc64le-flang-rhel-test while building llvm at step 6 "test-build-unified-tree-check-flang".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/157/builds/30776

Here is the relevant piece of the build log for the reference

Step 6 (test-build-unified-tree-check-flang) failure: test (failure)
******************** TEST 'Flang :: Semantics/modfile75.F90' FAILED ********************
Exit Code: 2

Command Output (stderr):
--
/home/buildbots/llvm-external-buildbots/workers/ppc64le-flang-rhel-test/ppc64le-flang-rhel-clang-build/build/bin/flang -c -fhermetic-module-files -DWHICH=1 /home/buildbots/llvm-external-buildbots/workers/ppc64le-flang-rhel-test/ppc64le-flang-rhel-clang-build/llvm-project/flang/test/Semantics/modfile75.F90 && /home/buildbots/llvm-external-buildbots/workers/ppc64le-flang-rhel-test/ppc64le-flang-rhel-clang-build/build/bin/flang -c -fhermetic-module-files -DWHICH=2 /home/buildbots/llvm-external-buildbots/workers/ppc64le-flang-rhel-test/ppc64le-flang-rhel-clang-build/llvm-project/flang/test/Semantics/modfile75.F90 && /home/buildbots/llvm-external-buildbots/workers/ppc64le-flang-rhel-test/ppc64le-flang-rhel-clang-build/build/bin/flang -fc1 -fdebug-unparse /home/buildbots/llvm-external-buildbots/workers/ppc64le-flang-rhel-test/ppc64le-flang-rhel-clang-build/llvm-project/flang/test/Semantics/modfile75.F90 | /home/buildbots/llvm-external-buildbots/workers/ppc64le-flang-rhel-test/ppc64le-flang-rhel-clang-build/build/bin/FileCheck /home/buildbots/llvm-external-buildbots/workers/ppc64le-flang-rhel-test/ppc64le-flang-rhel-clang-build/llvm-project/flang/test/Semantics/modfile75.F90 # RUN: at line 1
+ /home/buildbots/llvm-external-buildbots/workers/ppc64le-flang-rhel-test/ppc64le-flang-rhel-clang-build/build/bin/flang -c -fhermetic-module-files -DWHICH=1 /home/buildbots/llvm-external-buildbots/workers/ppc64le-flang-rhel-test/ppc64le-flang-rhel-clang-build/llvm-project/flang/test/Semantics/modfile75.F90
+ /home/buildbots/llvm-external-buildbots/workers/ppc64le-flang-rhel-test/ppc64le-flang-rhel-clang-build/build/bin/flang -c -fhermetic-module-files -DWHICH=2 /home/buildbots/llvm-external-buildbots/workers/ppc64le-flang-rhel-test/ppc64le-flang-rhel-clang-build/llvm-project/flang/test/Semantics/modfile75.F90
+ /home/buildbots/llvm-external-buildbots/workers/ppc64le-flang-rhel-test/ppc64le-flang-rhel-clang-build/build/bin/flang -fc1 -fdebug-unparse /home/buildbots/llvm-external-buildbots/workers/ppc64le-flang-rhel-test/ppc64le-flang-rhel-clang-build/llvm-project/flang/test/Semantics/modfile75.F90
+ /home/buildbots/llvm-external-buildbots/workers/ppc64le-flang-rhel-test/ppc64le-flang-rhel-clang-build/build/bin/FileCheck /home/buildbots/llvm-external-buildbots/workers/ppc64le-flang-rhel-test/ppc64le-flang-rhel-clang-build/llvm-project/flang/test/Semantics/modfile75.F90
error: Semantic errors in /home/buildbots/llvm-external-buildbots/workers/ppc64le-flang-rhel-test/ppc64le-flang-rhel-clang-build/llvm-project/flang/test/Semantics/modfile75.F90
/home/buildbots/llvm-external-buildbots/workers/ppc64le-flang-rhel-test/ppc64le-flang-rhel-clang-build/llvm-project/flang/test/Semantics/modfile75.F90:15:11: error: Must be a constant value
    integer(c_int) n
            ^^^^^
FileCheck error: '<stdin>' is empty.
FileCheck command line:  /home/buildbots/llvm-external-buildbots/workers/ppc64le-flang-rhel-test/ppc64le-flang-rhel-clang-build/build/bin/FileCheck /home/buildbots/llvm-external-buildbots/workers/ppc64le-flang-rhel-test/ppc64le-flang-rhel-clang-build/llvm-project/flang/test/Semantics/modfile75.F90

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