[libc][NFC] Skip adding dummy targets for skipped unit tests.

libc/cmake/modules/LLVMLibCTestRules.cmake

@@ -111,14 +111,6 @@ function(add_libc_unittest target_name)
     set(msg "Skipping unittest ${fq_target_name} as it has missing deps: "
             "${skipped_entrypoints_list}.")
     message(STATUS ${msg})
-    add_custom_target(${fq_target_name})
-
-    # A post build custom command is used to avoid running the command always.
-    add_custom_command(
-      TARGET ${fq_target_name}
-      POST_BUILD
-      COMMAND ${CMAKE_COMMAND} -E echo ${msg}
-    )
     return()
   endif()
 

libc/test/src/math/CMakeLists.txt

@@ -18,6 +18,9 @@ function(add_fp_unittest name)
 
   add_libc_unittest(${name} ${MATH_UNITTEST_UNPARSED_ARGUMENTS})
   get_fq_target_name(${name} fq_target_name)
+  if (NOT TARGET ${fq_target_name})
+    return()
+  endif()
   if(MATH_UNITTEST_NEED_MPFR)
     target_link_libraries(${fq_target_name} PRIVATE libcMPFRWrapper -lmpfr -lgmp)
   endif()