Add support for specifiying a language standard

    * docs/templates/bmake.txt:
    * templates/bmake.mpd:

Author: jwillemsen

docs/templates/bmake.txt

@@ -19,6 +19,7 @@ debug_prj = Indicates that the current template configuration is debug.  This is
 defines = Macros that are specific to a particular configuration.
 dllflags = Linker flags that are required to create a dynamic library.
 exeflags = Linker flags that are required to create an executable.
+languagestandard = Which version of ISO C++ standard to compile against (c++14, c++17, c++20, c++23)
 libflags = Flags that are required to create a static library.
 link = The name of the tool used to create dynamic libraries and executables.
 obj_ext = The extension given to object files.

templates/bmake.mpd

@@ -96,7 +96,8 @@ DLL_EXT      = <%dll_ext%>
 EXE_EXT      = <%exe_ext%>
 RC           = <%rc%>
 LIBFLAGS     = <%libflags%>
-CCFLAGS      = $(CC_CFLAGS)<%if(type_is_binary)%> $(BINARY_FLAGS)<%endif%><%if(compile_flags)%> <%compile_flags%><%endif%>
+CCFLAGS      = $(CC_CFLAGS)<%if(type_is_binary)%> $(BINARY_FLAGS)<%endif%><%if(compile_flags)%> <%compile_flags%><%endif%><%if(languagestandard)%> -std=<%languagestandard%><%endif%>
+
 
 <%if(use_vcl)%>
 STARTUP_LETTER = <%if(exename)%>w<%else%><%startup_letter%><%endif%>