Fix 'expected identifier or ( before numeric constant' error for true/false in GCC 11.2.0

[patrickmn]

Fixes

libtool: compile:  gcc -DHAVE_CONFIG_H -I. -I../../include/urweb -I./../../include/urweb -I/usr/include -Wall -Wunused-parameter -Werror -Wno-format-security -Wno-deprecated-declarations -U_FORTIFY_SOURCE -g -O2 -MT urweb.lo -MD -MP -MF .deps/urweb.Tpo -c urweb.c  -fPIC -DPIC -o .libs/urweb.o
In file included from /usr/include/unicode/utf8.h:37,
                 from urweb.c:23:
urweb.c: In function ‘uw_Basis_ensqlBool’:
urweb.c:3122:23: error: expected identifier or ‘(’ before numeric constant
 3122 |   static uw_Basis_int true = 1;
      |                       ^~~~
urweb.c:3123:23: error: expected identifier or ‘(’ before numeric constant
 3123 |   static uw_Basis_int false = 0;
      |                       ^~~~~
urweb.c:3126:20: error: lvalue required as unary ‘&’ operand
 3126 |     return (char *)&false;
      |                    ^
urweb.c:3128:20: error: lvalue required as unary ‘&’ operand
 3128 |     return (char *)&true;
      |                    ^
In file included from /usr/include/unicode/utf8.h:37,
                 from urweb.c:23:
urweb.c: In function ‘uw_Basis_stringToBool’:
urweb.c:3226:24: error: expected identifier or ‘(’ before numeric constant
 3226 |   static uw_Basis_bool true = uw_Basis_True;
      |                        ^~~~
urweb.c:3227:24: error: expected identifier or ‘(’ before numeric constant
 3227 |   static uw_Basis_bool false = uw_Basis_False;
      |                        ^~~~~
urweb.c:3230:12: error: lvalue required as unary ‘&’ operand
 3230 |     return &true;
      |            ^
urweb.c:3232:12: error: lvalue required as unary ‘&’ operand
 3232 |     return &false;
      |            ^
urweb.c: In function ‘uw_Basis_ensqlBool’:
urweb.c:3129:1: error: control reaches end of non-void function [-Werror=return-type]
 3129 | }
      | ^
urweb.c: In function ‘uw_Basis_stringToBool’:
urweb.c:3235:1: error: control reaches end of non-void function [-Werror=return-type]
 3235 | }
      | ^
cc1: all warnings being treated as errors
make[1]: *** [Makefile:535: urweb.lo] Error 1
make[1]: Leaving directory 'urweb/src/c'
make: *** [Makefile:432: all-recursive] Error 1

GCC 11.2.0 on Ubuntu 22.04 LTS