externals: Fix case spelling of libzip.

CMake is case senstive, so Libzip vs LIBZIP was a bug.
Upstream calls themself libzip, so let's pick this naming.

externals/find-modules/Findlibzip.cmake

@@ -0,0 +1,72 @@
+
+find_package(PkgConfig QUIET)
+pkg_check_modules(PC_libzip QUIET libzip)
+
+find_path(libzip_INCLUDE_DIR
+  NAMES zip.h
+  PATHS ${PC_libzip_INCLUDE_DIRS}
+  "$ENV{LIB_DIR}/include"
+  "$ENV{INCLUDE}"
+  /usr/local/include
+  /usr/include
+)
+find_path(libzip_INCLUDE_DIR_ZIPCONF
+  NAMES zipconf.h
+  HINTS ${PC_libzip_INCLUDE_DIRS}
+  "$ENV{LIB_DIR}/include"
+  "$ENV{LIB_DIR}/lib/libzip/include"
+  "$ENV{LIB}/lib/libzip/include"
+  /usr/local/lib/libzip/include
+  /usr/lib/libzip/include
+  /usr/local/include
+  /usr/include
+  "$ENV{INCLUDE}"
+)
+find_library(libzip_LIBRARY
+  NAMES zip
+  PATHS ${PC_libzip_LIBRARY_DIRS}
+  "$ENV{LIB_DIR}/lib" "$ENV{LIB}" /usr/local/lib /usr/lib
+)
+
+if (libzip_INCLUDE_DIR_ZIPCONF)
+  FILE(READ "${libzip_INCLUDE_DIR_ZIPCONF}/zipconf.h" _libzip_VERSION_CONTENTS)
+  if (_libzip_VERSION_CONTENTS)
+    STRING(REGEX REPLACE ".*#define LIBZIP_VERSION \"([0-9.]+)\".*" "\\1" libzip_VERSION "${_libzip_VERSION_CONTENTS}")
+  endif()
+  unset(_libzip_VERSION_CONTENTS)
+endif()
+
+set(libzip_VERSION ${libzip_VERSION} CACHE STRING "Version number of libzip")
+
+include(FindPackageHandleStandardArgs)
+find_package_handle_standard_args(libzip
+  FOUND_VAR libzip_FOUND
+  REQUIRED_VARS
+    libzip_LIBRARY
+    libzip_INCLUDE_DIR
+    libzip_INCLUDE_DIR_ZIPCONF
+    libzip_VERSION
+  VERSION_VAR libzip_VERSION
+)
+
+if(libzip_FOUND)
+  set(libzip_LIBRARIES ${libzip_LIBRARY})
+  set(libzip_INCLUDE_DIRS ${libzip_INCLUDE_DIR})
+  set(libzip_DEFINITIONS ${PC_libzip_CFLAGS_OTHER})
+endif()
+
+if(libzip_FOUND AND NOT TARGET libzip::libzip)
+  add_library(libzip::libzip UNKNOWN IMPORTED)
+  set_target_properties(libzip::libzip PROPERTIES
+    IMPORTED_LOCATION "${libzip_LIBRARY}"
+    INTERFACE_COMPILE_OPTIONS "${PC_libzip_CFLAGS_OTHER}"
+    INTERFACE_INCLUDE_DIRECTORIES "${libzip_INCLUDE_DIR}"
+  )
+endif()
+
+mark_as_advanced(
+    libzip_INCLUDE_DIR
+    libzip_INCLUDE_DIR_ZIPCONF
+    libzip_LIBRARY
+    libzip_VERSION
+)