doc: fix inaccuracies wrt --define and --force-define

The doc says that -Dfoo=bar is the same as %define foo "bar".  It is
not: the quotes are not added (and it makes a difference).

* doc/bison.texi (Tuning the Parser): Fix the definition of -D/-F
* src/getargs.c (usage): Likewise.

doc/bison.texi

@@ -10694,9 +10694,14 @@ it is not already defined, so that the debugging facilities are compiled.
 @itemx --define=@var{name}[=@var{value}]
 @itemx -F @var{name}[=@var{value}]
 @itemx --force-define=@var{name}[=@var{value}]
-Each of these is equivalent to @samp{%define @var{name} "@var{value}"}
-(@pxref{%define Summary}) except that Bison processes multiple definitions
-for the same @var{name} as follows:
+Each of these is equivalent to @samp{%define @var{name} @var{value}}
+(@pxref{%define Summary}).  Note that the delimiters are part of
+@var{value}: @option{-Dapi.value.type=union},
+@option{-Dapi.value.type=@{union@}} and @option{-Dapi.value.type="union"}
+correspond to @samp{%define api.value.type union}, @samp{%define
+api.value.type @{union@}} and @samp{%define api.value.type "union"}.
+
+Bison processes multiple definitions for the same @var{name} as follows:
 
 @itemize
 @item

src/getargs.c

@@ -404,10 +404,10 @@ Tuning the Parser:\n\
   -t, --debug                      instrument the parser for tracing\n\
                                    same as '-Dparse.trace'\n\
       --locations                  enable location support\n\
-  -D, --define=NAME[=VALUE]        similar to '%define NAME \"VALUE\"'\n\
-  -F, --force-define=NAME[=VALUE]  override '%define NAME \"VALUE\"'\n\
+  -D, --define=NAME[=VALUE]        similar to '%define NAME VALUE'\n\
+  -F, --force-define=NAME[=VALUE]  override '%define NAME VALUE'\n\
   -p, --name-prefix=PREFIX         prepend PREFIX to the external symbols\n\
-                                   deprecated by '-Dapi.prefix=PREFIX'\n\
+                                   deprecated by '-Dapi.prefix={PREFIX}'\n\
   -l, --no-lines                   don't generate '#line' directives\n\
   -k, --token-table                include a table of token names\n\
   -y, --yacc                       emulate POSIX Yacc\n\