#1167 Use the make -n parsing for C++ compilers, and document the new option

doc/ale-c.txt

@@ -31,7 +31,18 @@ g:ale_c_build_dir                                           *g:ale_c_build_dir*
   database (it can be useful if multiple builds are in multiple build
   subdirectories in the project tree).
   This feature is also most useful for the clang tools linters, wrapped
-  aroung LibTooling (namely clang-tidy here)
+  around LibTooling (namely clang-tidy here)
+
+
+g:ale_c_parse_makefile                                 *g:ale_c_parse_makefile*
+                                                       *b:ale_c_parse_makefile*
+  Type: |Number|
+  Default: `0`
+
+  If set to `1`, ALE will run `make -n` to automatically determine flags to
+  set for C or C++ compilers. This can make it easier to determine the correct
+  build flags to use for different files.
+
 
 ===============================================================================
 clang                                                             *ale-c-clang*

doc/ale-cpp.txt

@@ -5,8 +5,11 @@ ALE C++ Integration                                           *ale-cpp-options*
 ===============================================================================
 Global Options
 
-The |g:ale_c_build_dir_names| and |g:ale_c_build_dir| also apply to some C++
-linters too.
+The following C options also apply to some C++ linters too.
+
+* |g:ale_c_build_dir_names|
+* |g:ale_c_build_dir|
+* |g:ale_c_parse_makefile|
 
 
 ===============================================================================