Remove '-Werror=implicit-function-declaration'

Change-Id: I5f2b21c868c4db11f62c3cb2e350c40cd3a4b882
diff --git a/Source/GmmLib/Linux.cmake b/Source/GmmLib/Linux.cmake
index 2ff681a..fd62b4a 100644
--- a/Source/GmmLib/Linux.cmake
+++ b/Source/GmmLib/Linux.cmake
@@ -34,7 +34,6 @@
     -Wno-parentheses
     -Wno-missing-braces
     -Wno-sign-compare
-    -Werror=implicit-function-declaration
     -Werror=address
     -Werror=format-security
     -Werror=non-virtual-dtor