Require Xcode >= 11.2 on macOS 10.15 (Catalina)

- As detailed in a previous CL, Xcode 11.0-1 exhibited a -fstack-check
  bug on 10.15 Catalina that broke alignment for at least AVX
  instructions causing segfaults from within Eigen.
- As Xcode 11.2 fixes this issue, and is probably a more reliable fix
  than -fno-stack-check, we now require the user update in this case.

Change-Id: I482748fe5f40f82e7daf4da133cdfabbd95ffc89

cmake/DetectBrokenStackCheckMacOSXcodePairing.cmake

@@ -0,0 +1,83 @@
+# Ceres Solver - A fast non-linear least squares minimizer
+# Copyright 2019 Google Inc. All rights reserved.
+# http://ceres-solver.org/
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions are met:
+#
+# * Redistributions of source code must retain the above copyright notice,
+#   this list of conditions and the following disclaimer.
+# * Redistributions in binary form must reproduce the above copyright notice,
+#   this list of conditions and the following disclaimer in the documentation
+#   and/or other materials provided with the distribution.
+# * Neither the name of Google Inc. nor the names of its contributors may be
+#   used to endorse or promote products derived from this software without
+#   specific prior written permission.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+# AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+# ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+# LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+# CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+# SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+# INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+# CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+# ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+# POSSIBILITY OF SUCH DAMAGE.
+#
+# Author: alexs.mac@gmail.com (Alex Stewart)
+
+# As detailed in [1] the combination of macOS 10.15.x (Catalina) and
+# Xcode 11.0-1 enables by default a broken version of -fstack-check which
+# can break the alignment requirements for SIMD instructions resulting in
+# segfaults from within Eigen. This issue was apparently fixed in Xcode 11.2
+# despite not appearing in the official release notes.
+#
+# Although this can be worked around by compiling with -fno-stack-check, we
+# instead prevent generation as the update to Xcode 11.2 is free and failing
+# to include -fno-stack-check *everywhere* could still result in random
+# segfaults.
+#
+# [1]: https://forums.developer.apple.com/thread/121887
+function(detect_broken_stack_check_macos_xcode_pairing)
+  if (NOT APPLE)
+    return()
+  endif()
+
+  execute_process(COMMAND sw_vers -productVersion
+    OUTPUT_VARIABLE MACOS_VERSION
+    ERROR_QUIET
+    OUTPUT_STRIP_TRAILING_WHITESPACE)
+
+  if (MACOS_VERSION VERSION_LESS 10.15)
+    # Only 10.15 (Catalina) is likely to be affected, irrespective of the Xcode
+    # version. Although it is possible to recreate the issue on 10.14 (Mojave)
+    # and Xcode 11.0-1 if -fstack-check is forced on, this is not the default.
+    return()
+  endif()
+
+  execute_process(COMMAND xcodebuild -version
+    OUTPUT_VARIABLE XCODE_VERSION
+    ERROR_QUIET
+    OUTPUT_STRIP_TRAILING_WHITESPACE)
+  string(REGEX MATCH "Xcode [0-9\\.]+" XCODE_VERSION "${XCODE_VERSION}")
+  string(REGEX REPLACE "Xcode ([0-9\\.]+)" "\\1" XCODE_VERSION "${XCODE_VERSION}")
+
+  if ((XCODE_VERSION VERSION_EQUAL 11.0) OR
+      (XCODE_VERSION VERSION_EQUAL 11.1))
+    message(FATAL_ERROR "Detected macOS version: ${MACOS_VERSION} and "
+      "Xcode version: ${XCODE_VERSION} which combined exhibit an "
+      "-fstack-check bug which can break alignment requirements for at least "
+      "AVX instructions as detailed here [1]."
+      "\n"
+      "This bug affected Xcode 11.0 and 11.1 but only when used with 10.15 "
+      "(Catalina), and was fixed in Xcode 11.2. Without the fix in place, "
+      "random segfaults will occur in Eigen operations used by Ceres that use "
+      "AVX instructions."
+      "\n"
+      "Please update to at least Xcode 11.2."
+      "\n"
+      "[1]: https://forums.developer.apple.com/thread/121887")
+  endif()
+endfunction()