[libc][obvious] fix comparison test cmake

[michaelrj]

Summary

The name of the libc target changed, this patch updates the cmake for
the string to float comparison test to use the correct name.

libc/test/src/__support/CMakeLists.txt

 
 add_executable(
   libc_str_to_float_comparison_test
   str_to_float_comparison_test.cpp
 )
 
 target_link_libraries(libc_str_to_float_comparison_test
   PRIVATE
-    llvmlibc
+    "${LIBC_TARGET}"
 )
 
 add_executable(
   libc_system_str_to_float_comparison_test
   str_to_float_comparison_test.cpp
 )
 
 set(float_test_file ${CMAKE_CURRENT_SOURCE_DIR}/str_to_float_comparison_data.txt)