base gcc does not understand -Wwrite-strings and errors out.

Index: CMakeLists.txt
--- CMakeLists.txt.orig
+++ CMakeLists.txt
@@ -768,7 +768,7 @@ if(CMAKE_C_COMPILER_IS_GCC OR CMAKE_C_COMPILER_IS_CLAN
       -O2 \
       -fvisibility=hidden \
       -Wno-deprecated -Wall -Wunknown-pragmas -Wextra -Winit-self -Wunused -Wno-div-by-zero \
-      -Wundef -Wpointer-arith -Wtype-limits -Wwrite-strings -Wreturn-type \
+      -Wundef -Wpointer-arith -Wtype-limits -Wreturn-type \
       -Wold-style-definition -Wstrict-prototypes"
   )
   if(LIBICAL_DEVMODE)
@@ -805,7 +805,7 @@ if(CMAKE_CXX_COMPILER_IS_GCC OR CMAKE_CXX_COMPILER_IS_
       -O2 \
       -fvisibility=hidden \
       -Weffc++ -Wno-deprecated -Wall -Wextra -Woverloaded-virtual -Winit-self -Wunused \
-      -Wno-div-by-zero -Wundef -Wpointer-arith -Wtype-limits -Wwrite-strings -Wreturn-type"
+      -Wno-div-by-zero -Wundef -Wpointer-arith -Wtype-limits -Wreturn-type"
   )
   if(LIBICAL_DEVMODE)
     set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Werror")
