PDAL: enable use of system libunwind, drop dependency of port

This doesn't solve the problem with Xcode 15, automatically linking to
MacPorts' libunwind, but it makes it possible to some degree avoid
installing the port in the first place.

See https://trac.macports.org/ticket/68250
See https://trac.macports.org/ticket/66250

gis/pdal/Portfile

@@ -7,7 +7,7 @@ PortGroup           github        1.0
 PortGroup           openssl       1.0
 
 github.setup        PDAL PDAL 2.5.6
-revision            1
+revision            2
 categories          gis
 license             BSD
 
@@ -45,17 +45,24 @@ depends_lib-append  port:geos \
                     port:zlib \
                     port:zstd \
                     port:libxml2 \
-                    port:curl \
-                    port:libunwind
+                    port:curl
 
-patchfiles-append   patch-powerpc.diff
+patchfiles-append   patch-powerpc.diff \
+                    patch-libunwind-cmake.diff
+
+# Starting with Xcode 15, the port libunwind is causing crashes,
+# see https://trac.macports.org/ticket/68250 and https://trac.macports.org/ticket/66250.
+if {[vercmp $xcodeversion >= 15.0]} {
+    conflicts       libunwind
+}
 
 configure.args      -DWITH_ZSTD=ON \
                     -DWITH_ZLIB=ON \
                     -DWITH_LZMA=OFF \
                     -DWITH_TESTS=OFF \
                     -DBUILD_TOOLS_NITFWRAP=OFF \
-                    -DWITH_COMPLETION=OFF
+                    -DWITH_COMPLETION=OFF \
+                    -DWITH_BACKTRACE=OFF
 
 configure.args-append \
                     -DBUILD_PLUGIN_CPD=OFF \

gis/pdal/files/patch-libunwind-cmake.diff

@@ -0,0 +1,70 @@
+Committed 2023-09-29 upstreams to master:
+https://github.com/PDAL/PDAL/commit/a14f8648a2f43296e032901d75969ce9070dc563
+
+--- cmake/modules/FindLibunwind.cmake.orig
++++ cmake/modules/FindLibunwind.cmake
+@@ -2,14 +2,21 @@
+ # ~~~~~~~~~
+ # CMake module to search for LIBUNWIND
+ #
+- 
+-find_library(LIBUNWIND_LIBRARY unwind)
++
+ find_path(LIBUNWIND_INCLUDE_DIR libunwind.h)
+
+-find_package_handle_standard_args(LIBUNWIND REQUIRED_VARS
+-    LIBUNWIND_LIBRARY LIBUNWIND_INCLUDE_DIR)
++if(NOT APPLE)
++  find_library(LIBUNWIND_LIBRARY unwind)
++  find_package_handle_standard_args(
++    LIBUNWIND REQUIRED_VARS LIBUNWIND_LIBRARY LIBUNWIND_INCLUDE_DIR)
++else()
++  find_package_handle_standard_args(LIBUNWIND
++                                    REQUIRED_VARS LIBUNWIND_INCLUDE_DIR)
++endif()
+
+-if (LIBUNWIND_FOUND)
+-  set(LIBUNWIND_LIBRARIES ${LIBUNWIND_LIBRARY})
++if(LIBUNWIND_FOUND)
++  if(LIBUNWIND_LIBRARY)
++    set(LIBUNWIND_LIBRARIES ${LIBUNWIND_LIBRARY})
++  endif()
+   set(LIBUNWIND_INCLUDE_DIRS ${LIBUNWIND_INCLUDE_DIR})
+ endif()
+
+
+Make backtrace optional, committed 2023-10-02 upstreams to master:
+https://github.com/PDAL/PDAL/commit/95c5e378d6b31b88cbdbabcb75a71ffe9d6a1c10
+
+--- cmake/options.cmake.orig
++++ cmake/options.cmake
+@@ -109,6 +109,11 @@
+     "Choose if PDAL should be built with Abseil support for testing" FALSE)
+ add_feature_info("Abseil debugging support " WITH_ABSEIL "unit tests")
+
++option(WITH_BACKTRACE
++    "Build with backtrace" ON)
++add_feature_info("Backtrace" WITH_BACKTRACE
++    "build with backtrace (Libunwind/Libexecinfo) support")
++
+ #
+ # Choose dependent options
+ #
+
+
+--- pdal/util/CMakeLists.txt.orig
++++ pdal/util/CMakeLists.txt
+@@ -11,10 +11,10 @@
+ include(${PDAL_CMAKE_DIR}/unwind.cmake)
+ include(${PDAL_CMAKE_DIR}/utfcpp.cmake)
+
+-if(LIBUNWIND_FOUND)
++if(LIBUNWIND_FOUND AND WITH_BACKTRACE)
+     set(BACKTRACE_SOURCE BacktraceUnwind.cpp)
+     set(BACKTRACE_LIBRARIES ${LIBUNWIND_LIBRARIES} ${CMAKE_DL_LIBS})
+-elseif(LIBEXECINFO_FOUND)
++elseif(LIBEXECINFO_FOUND AND WITH_BACKTRACE)
+     set(BACKTRACE_SOURCE BacktraceExecinfo.cpp)
+     set(BACKTRACE_LIBRARIES ${LIBEXECINFO_LIBRARIES} ${CMAKE_DL_LIBS})
+ else()
+