Index: MultiSource/Applications/siod/CMakeLists.txt
===================================================================
--- MultiSource/Applications/siod/CMakeLists.txt
+++ MultiSource/Applications/siod/CMakeLists.txt
@@ -1,4 +1,4 @@
-list(APPEND CPPFLAGS -D__USE_MISC -D__USE_GNU -D__USE_SVID -D__USE_XOPEN_EXTENDED -D__USE_XOPEN -Dunix)
+list(APPEND CPPFLAGS -D__USE_MISC -D__USE_GNU -D__USE_SVID -D__USE_XOPEN_EXTENDED -D__USE_XOPEN -Dunix -Wno-implicit-function-declaration)
 list(APPEND LDFLAGS -lm)
 set(RUN_OPTIONS -v1 test.scm)
 llvm_multisource(siod)
Index: MultiSource/Benchmarks/MiBench/office-ispell/CMakeLists.txt
===================================================================
--- MultiSource/Benchmarks/MiBench/office-ispell/CMakeLists.txt
+++ MultiSource/Benchmarks/MiBench/office-ispell/CMakeLists.txt
@@ -1,4 +1,4 @@
-list(APPEND CPPFLAGS -Dconst=)
+list(APPEND CPPFLAGS  -Wno-implicit-function-declaration -Dconst=)
 list(APPEND LDFLAGS -lm)
 set(RUN_OPTIONS -a -d americanmed+ < large.txt)
 llvm_multisource(office-ispell)
Index: MultiSource/Benchmarks/Prolangs-C/archie-client/CMakeLists.txt
===================================================================
--- MultiSource/Benchmarks/Prolangs-C/archie-client/CMakeLists.txt
+++ MultiSource/Benchmarks/Prolangs-C/archie-client/CMakeLists.txt
@@ -1,4 +1,5 @@
 include(CheckFunctionExists)
+list(APPEND CPPFLAGS -Wno-implicit-function-declaration)
 check_function_exists(re_comp HAVE_RE_COMP)
 
 if(HAVE_RE_COMP)
Index: MultiSource/Benchmarks/Prolangs-C/plot2fig/CMakeLists.txt
===================================================================
--- MultiSource/Benchmarks/Prolangs-C/plot2fig/CMakeLists.txt
+++ MultiSource/Benchmarks/Prolangs-C/plot2fig/CMakeLists.txt
@@ -1,5 +1,6 @@
 include(CheckFunctionExists)
 check_function_exists(re_comp HAVE_RE_COMP)
+list(APPEND CPPFLAGS -Wno-implicit-function-declaration)
 if(HAVE_RE_COMP)
   list(APPEND LDFLAGS -lm)
   llvm_multisource(plot2fig)
Index: SingleSource/Regression/C/gcc-c-torture/execute/CMakeLists.txt
===================================================================
--- SingleSource/Regression/C/gcc-c-torture/execute/CMakeLists.txt
+++ SingleSource/Regression/C/gcc-c-torture/execute/CMakeLists.txt
@@ -1,7 +1,7 @@
 add_subdirectory(ieee)
 
 # GCC C Torture Suite is conventionally run without warnings
-list(APPEND CFLAGS "-w")
+list(APPEND CFLAGS  -Wno-implicit-function-declaration -w)
 
 set(TestsToSkip)