Disallow evil compilation

-fpermissive allows nasty things that are (apparently) needed on
Windows, so only enable it there.

vla are evil, so don't just warn but error on it.

remove duplicate -Wno-unknown-pragmas

CMakeLists.txt

@@ -212,11 +212,10 @@ if (CMAKE_CXX_COMPILER_ID MATCHES "Clang")
 endif()
 
 if (NOT MSVC_VERSION)
-	add_compile_options(-Wall -Wextra -Wno-unknown-pragmas)
-	# vla are evil
-	add_compile_options(-Wvla)
-	add_compile_options($<$<COMPILE_LANGUAGE:CXX>:-fpermissive>)
-	add_compile_options(-Wno-unused-function -Wno-deprecated-declarations -Wno-unknown-pragmas)
+  add_compile_options(-Wall -Wextra -Wno-unknown-pragmas)
+  # vla are evil
+  add_compile_options(-Werror=vla)
+  add_compile_options(-Wno-unused-function -Wno-deprecated-declarations)
 endif()
 
 include(cmake/coverage.cmake)

cmake/win32.cmake

@@ -9,6 +9,7 @@ set(gtest_force_shared_crt ON CACHE BOOL "" FORCE)
 if(NOT MSVC_VERSION)
   add_compile_options($<$<COMPILE_LANGUAGE:C>:-Wno-bad-function-cast>)
   add_compile_options($<$<COMPILE_LANGUAGE:C>:-Wno-cast-function-type>)
+  add_compile_options($<$<COMPILE_LANGUAGE:CXX>:-fpermissive>)
   # unlike unix where you get a *single* compiler ID string in .comment
   # GNU ld sees fit to merge *all* the .ident sections in object files
   # to .r[o]data section one after the other!