Add a features.h to auto enable _DEFAULT_SOURCE

Unless __STRICT_ANSI__ is defined (as it is when running the compiler in
--std=c89 or --std=c99, but not when running it without any specific
args), we can enable these by default and behave like most other
systems. I don't know why no one has done this yet despite suggesting it
multiple times and people prefer to #define _BSD_SOURCE manually
everywhere.

Remove all places in our Jamfiles and sources where it had been defined.
_DEFAULT_SOURCE is now enabled by default for all sources of Haiku, since we
let the compiler use GNU extensions (no strict C standard specified on
command line)

Use _DEFAULT_SOURCE as the define name to match current versions of
glibc. Enable it if _BSD_SOURCE is #defined in compiler flags, for
backward compatibility.

Change-Id: I6db04da5f6db437723cdfba3478f5094a69d7727
Reviewed-on: https://review.haiku-os.org/c/1633
Reviewed-by: Jérôme Duval <[email protected]>

src/bin/fwcontrol/Jamfile

@@ -2,7 +2,6 @@ SubDir HAIKU_TOP src bin fwcontrol ;
 
 UseHeaders [ FDirName $(HAIKU_TOP) headers compatibility bsd ] : true ;
 UsePrivateHeaders firewire ;
-SubDirCcFlags [ FDefines _BSD_SOURCE=1 ] ;
 
 BinCommand fwcontrol :
 	eui64.c

src/bin/multiuser/Jamfile

@@ -7,7 +7,6 @@ UsePrivateHeaders kernel ;
 UsePrivateHeaders libroot ;
 UsePrivateHeaders shared ;
 UseHeaders [ FDirName $(HAIKU_TOP) headers compatibility bsd ] : true ;
-SubDirC++Flags [ FDefines _BSD_SOURCE=1 ] ;
 
 StaticLibrary libmultiuser_utils.a : multiuser_utils.cpp ;
 

src/bin/network/ftpd/Jamfile

@@ -2,7 +2,6 @@ SubDir HAIKU_TOP src bin network ftpd ;
 
 UseHeaders [ FDirName $(HAIKU_TOP) headers compatibility bsd ] : true ;
 UseHeaders $(SUBDIR) : true ;
-SubDirCcFlags [ FDefines _BSD_SOURCE=1 ] ;
 
 BinCommand ftpd :
 	ftpd.c

src/bin/network/ifconfig/Jamfile

@@ -5,8 +5,6 @@ UsePrivateHeaders net ;
 UseHeaders [ FDirName $(HAIKU_TOP) src libs compat ] : true ;
 UseHeaders [ FDirName $(HAIKU_TOP) src libs compat freebsd_wlan ] : true ;
 
-SubDirC++Flags [ FDefines _BSD_SOURCE=1 ] ;
-
 BinCommand ifconfig :
 	ifconfig.cpp
 	MediaTypes.cpp

src/bin/network/telnet/Jamfile

@@ -6,7 +6,7 @@ UseHeaders [ FDirName $(HAIKU_TOP) src libs libtelnet ] : false ;
 
 UseBuildFeatureHeaders ncurses ;
 
-local defines = [ FDefines USE_TERMIO=1 OLD_ENVIRON=1 ENV_HACK=1 _BSD_SOURCE=1 ] ;
+local defines = [ FDefines USE_TERMIO=1 OLD_ENVIRON=1 ENV_HACK=1 ] ;
 
 SubDirCcFlags $(defines) ;
 SubDirC++Flags $(defines) ;

src/bin/network/telnetd/Jamfile

@@ -5,7 +5,7 @@ UseHeaders [ FDirName $(HAIKU_TOP) headers compatibility bsd ] : true ;
 UseHeaders [ FDirName $(HAIKU_TOP) src libs ] : true ;
 UseHeaders [ FDirName $(HAIKU_TOP) src libs libtelnet ] : false ;
 
-local defines = [ FDefines USE_TERMIO=1 _BSD_SOURCE=1 ] ;
+local defines = [ FDefines USE_TERMIO=1 ] ;
 
 SubDirCcFlags $(defines) ;
 SubDirC++Flags $(defines) ;