Tests/RunCMake/LinkStatic: Update for Xcode 26.4

`libtool` with Xcode 26.4 no longer fails on a missing object file:

    $ libtool -static -o libfoo.a foo.o missing.o ; echo exit-code=$?
    libtool: warning: file not found 'missing.o'
    exit-code=0

as it did with Xcode 26.3 and below:

    $ libtool -static -o libfoo.a foo.o missing.o ; echo exit-code=$?
    error: libtool: can't open file: missing.o (No such file or directory)
    exit-code=1

Use a bad flag instead.

Tests/RunCMake/LinkStatic/CMAKE_STATIC_LINKER_FLAGS.cmake

@@ -4,6 +4,8 @@ enable_language(C)
 set(obj "${CMAKE_C_OUTPUT_EXTENSION}")
 if(BORLAND)
   set(pre -)
+elseif(XCODE)
+  set(pre --badflag=)
 endif()
 
 set(CMAKE_STATIC_LINKER_FLAGS ${pre}BADFLAG${obj})

Tests/RunCMake/LinkStatic/CMAKE_STATIC_LINKER_FLAGS_CONFIG.cmake

@@ -4,6 +4,8 @@ enable_language(C)
 set(obj "${CMAKE_C_OUTPUT_EXTENSION}")
 if(BORLAND)
   set(pre -)
+elseif(XCODE)
+  set(pre --badflag=)
 endif()
 
 # CMAKE_STATIC_LINKER_FLAGS_<CONFIG> variant

Tests/RunCMake/LinkStatic/STATIC_LIBRARY_FLAGS.cmake

@@ -4,6 +4,8 @@ enable_language(C)
 set(obj "${CMAKE_C_OUTPUT_EXTENSION}")
 if(BORLAND)
   set(pre -)
+elseif(XCODE)
+  set(pre --badflag=)
 endif()
 
 add_library(StaticLinkFlags STATIC LinkOptionsLib.c)

Tests/RunCMake/LinkStatic/STATIC_LIBRARY_OPTIONS.cmake

@@ -4,6 +4,8 @@ enable_language(C)
 set(obj "${CMAKE_C_OUTPUT_EXTENSION}")
 if(BORLAND)
   set(pre -)
+elseif(XCODE)
+  set(pre --badflag=)
 endif()
 
 add_library(StaticLinkOptions STATIC LinkOptionsLib.c)