Fixed various problems with the latest stdbool.h changes, including stdbool.h itself:

- SupportDefs.h only includes stdbool.h if included from C
- stdbool.h for C++ now includes a macro for "bool" as defined by that header
- stdbool.h does nothing if __bool_true_false_are_defined is already defined
- stdbool.h no longer defines a _Bool enum, but defines _Bool as unsigned char, as
  previously done by SupportDefs.h (the previous version changed the size).
- The gensyscalls Jamfile now preprocesses its headers in C++ mode so that "bool"
  stays "bool", and doesn't become _Bool.


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@12042 a95241bf-73f2-0310-859d-f6bbb57e9c96

src/tools/gensyscalls/Jamfile

@@ -131,7 +131,7 @@ rule Preprocess
 
 actions Preprocess 
 {
-	$(CC) -E "$(2)" $(CCFLAGS) $(CCDEFS) $(CCHDRS) -o "$(1)" ;
+	$(C++) -xc++ -E "$(2)" $(CCFLAGS) $(CCDEFS) $(CCHDRS) -o "$(1)" ;
 }
 
 Preprocess $(syscallsHeaderPP) : $(syscallsHeader) ;