Cherry-pick d192a5a. rdar://115294369

    Fix the visionOS build
    https://bugs.webkit.org/show_bug.cgi?id=261369
    rdar://115202809

    Reviewed by Tim Horton.

    * Source/WebKit/Configurations/WebKit.xcconfig:

    Use `-weak_framework` to link MRUIKit, since the framework is not present in all configurations.

    Canonical link: https://commits.webkit.org/267826@main

Canonical link: https://commits.webkit.org/267815.5@safari-7617.1.8-branch

Source/WebKit/Configurations/WebKit.xcconfig

@@ -138,8 +138,8 @@ WK_UIKIT_LDFLAGS_cocoatouch = -framework UIKit;
 // it's impossible to tell the difference between visionOS and iOS with the latter.
 // Don't copy this unless you also need to differentiate!
 WK_MRUIKIT_LDFLAGS = $(WK_MRUIKIT_LDFLAGS_$(PLATFORM_NAME));
-WK_MRUIKIT_LDFLAGS_xros = -framework MRUIKit;
-WK_MRUIKIT_LDFLAGS_xrsimulator = -framework MRUIKit;
+WK_MRUIKIT_LDFLAGS_xros = -weak_framework MRUIKit;
+WK_MRUIKIT_LDFLAGS_xrsimulator = -weak_framework MRUIKit;
 
 WK_UNIFORM_TYPE_IDENTIFIERS_LDFLAGS = $(WK_UNIFORM_TYPE_IDENTIFIERS_LDFLAGS_$(WK_PLATFORM_NAME));
 WK_UNIFORM_TYPE_IDENTIFIERS_LDFLAGS_iphoneos = $(WK_UNIFORM_TYPE_IDENTIFIERS_LDFLAGS$(WK_IOS_14));