[libc] Fix PrintfMatcher Cmake Rule

[michaelrj]

Summary

The PrintfMatcher depends on printf which is in stdio. Stdio is
currently fullbuild only, but the matcher wasn't, causing failing builds
when fullbuild was off. This patch adds the fullbuild condition to the
PrintfMatcher cmake.

libc/utils/UnitTest/CMakeLists.txt

 target_include_directories(LibcMemoryHelpers PUBLIC ${LIBC_SOURCE_DIR})
 target_link_libraries(LibcMemoryHelpers LibcUnitTest)
 add_dependencies(
   LibcMemoryHelpers
   LibcUnitTest
   libc.src.__support.CPP.array_ref
 )
 
+if(NOT LLVM_LIBC_FULL_BUILD) # TODO(michaelrj): make a more permanant solution.
+  return()
+endif()
+
+#currently stdio is fullbuild only, so this matcher that depends on a piece of
+#printf also has to be fullbuild only.
+
 add_library(
   LibcPrintfHelpers
     PrintfMatcher.h
     PrintfMatcher.cpp
 )
 target_include_directories(LibcPrintfHelpers PUBLIC ${LIBC_SOURCE_DIR})
 target_link_libraries(LibcPrintfHelpers LibcUnitTest)
 add_dependencies(
   LibcPrintfHelpers
   LibcUnitTest
   libc.utils.UnitTest.string_utils
   libc.src.stdio.printf_core.core_structs
 )