Conan: Use the 'shared' option value of the Qt build

Default to the value of the prebuilt Qt build.

The 'default' needs to be added as valid option in the list which
will be used by default if no value is given by the user or via
the conan profile.

The user is still able to override this via the profile or from
command line if needed:

  "conan install ... -o shared=False"

CMakeCache.txt:

  - "conan install ..."
    - BUILD_SHARED_LIBS:BOOL=ON
  - "conan install ... -o shared=True"
    - BUILD_SHARED_LIBS:BOOL=ON
  - "conan install ... -o shared=False"
    - BUILD_SHARED_LIBS:BOOL=OFF

Pick-to: 6.1
Task-number: QTBUG-90901
Change-Id: I991516a804875475991e27c7265693b3a7adec5d
Reviewed-by: Joerg Bornemann <joerg.bornemann@qt.io>

conanfile.py

@@ -44,9 +44,9 @@ class QtCoAP(ConanFile):
                   "The full specification can be found in RFC 7252"
     topics = ("qt", "qt6", "CoAP", "IoT", "M2M")
     settings = "os", "compiler", "build_type", "arch"
-    options = {"shared": [True, False],
+    options = {"shared": [True, False, "default"],
                "qt6": "ANY"}  # this is needed to model unique package_id for the Add-on build per used Qt6 version
-    default_options = {"shared": False,
+    default_options = {"shared": "default",  # default: Use the value of the Qt build
                        "qt6": None}
     exports_sources = "*", "!conan*.*"
 
@@ -88,6 +88,10 @@ class QtCoAP(ConanFile):
         install_dir = os.path.join(os.getcwd(), "_install_tmp")
         cmake.definitions["CMAKE_INSTALL_PREFIX"] = install_dir
 
+        # Use the value of the Qt build
+        if self.options.shared.value == "default":
+            del cmake.definitions["BUILD_SHARED_LIBS"]
+
         cmake_toolchain_file = os.environ.get("CMAKE_TOOLCHAIN_FILE")
         if cmake_toolchain_file:
             cmake.definitions["CMAKE_TOOLCHAIN_FILE"] = cmake_toolchain_file