Disable implicit function warnings

This hopefully addresses the issue in:
https://lab.llvm.org/buildbot/#/builders/57/builds/17109
diff --git a/SingleSource/UnitTests/CMakeLists.txt b/SingleSource/UnitTests/CMakeLists.txt
index b146c03..b4fd5ba 100644
--- a/SingleSource/UnitTests/CMakeLists.txt
+++ b/SingleSource/UnitTests/CMakeLists.txt
@@ -6,6 +6,9 @@
 add_subdirectory(Threads)
 add_subdirectory(Vector)
 add_subdirectory(Vectorizer)
+
+list(APPEND CFLAGS -Wno-implicit-function-declaration)
+
 # FIXME: Disable SJLJ tests for now, until EH edges are represented.
 # add_subdirectory(SetjmpLongjmp)
 if(TARGET_OS STREQUAL "Darwin")
diff --git a/SingleSource/UnitTests/Makefile b/SingleSource/UnitTests/Makefile
index 3a9a7cb..ac7badd 100644
--- a/SingleSource/UnitTests/Makefile
+++ b/SingleSource/UnitTests/Makefile
@@ -58,5 +58,7 @@
 XCORE_TARGET_NEEDS_MEMORY := 1
 endif
 
+CFLAGS += -Wno-implicit-function-declaration
+
 LDFLAGS += -lstdc++
 include $(LEVEL)/SingleSource/Makefile.singlesrc