Add support for building <stubbed>libroot.so.

* <stubbed>libroot.so is a shared library which contains all the symbols
  from libroot, but without any code. This library will be required by
  the (to be introduced) stage0 of the bootstrap process, in order to
  be able to link the shared gcc syslibs (libstdc++.so, libsupc++.so
  and libgcc_s.so).

src/system/libroot/Jamfile

@@ -125,3 +125,4 @@ for architectureObject in [ MultiArchSubDirSetup ] {
 SubInclude HAIKU_TOP src system libroot add-ons ;
 SubInclude HAIKU_TOP src system libroot os ;
 SubInclude HAIKU_TOP src system libroot posix ;
+SubInclude HAIKU_TOP src system libroot stubbed ;

src/system/libroot/stubbed/Jamfile

@@ -0,0 +1,28 @@
+SubDir HAIKU_TOP src system libroot stubbed ;
+
+local architectureObject ;
+for architectureObject in [ MultiArchSubDirSetup ] {
+	on $(architectureObject) {
+
+		UsePrivateSystemHeaders ;
+
+		# Build <stubbed>libroot.so, containing only empty symbols.
+		local stubsSource ;
+		if $(TARGET_PACKAGING_ARCH) = x86_gcc2 {
+			stubsSource = [ FGristFiles libroot_stubs_legacy.c ] ;
+		} else {
+			stubsSource = [ FGristFiles libroot_stubs.c ] ;
+		}
+		local stubsObject = $(stubsSource:S=$(SUFOBJ)) ;
+		CCFLAGS on $(stubsObject) = -Wno-missing-prototypes -fno-builtin ;
+		Depends $(stubsObject) : $(stubsSource) ;
+		Objects $(stubsSource) ;
+		local stubbedLibroot
+			= [ MultiArchDefaultGristFiles libroot.so : stubbed ] ;
+		local versionScript
+			= [ FDirName $(HAIKU_TOP) src system libroot libroot_versions ] ;
+		LINKFLAGS on $(stubbedLibroot)
+			= -shared -soname=libroot.so --version-script $(versionScript) ;
+		Ld $(stubbedLibroot) : $(stubsObject) ;
+	}
+}

src/system/libroot/stubbed/generate_stubs.py

@@ -0,0 +1,65 @@
+#! /usr/bin/env python
+
+import sys;
+
+dataSymbolsByAddress = {}
+versionedDataSymbolsByName = {}
+functionSymbolsByAddress = {}
+versionedFunctionSymbolsByName = {}
+
+for line in sys.stdin.readlines():
+	if line[0] != '0':
+		# ignore lines without an address
+		continue
+
+	(address, type, symbol) = line.split()
+
+	# select interesting types of symbols
+	if not type in 'BCDGRSTuVvWw':
+		continue
+
+	# drop symbols from legacy compiler that contain a dot (those produce
+	# syntax errors)
+	if '.' in symbol:
+		continue
+
+	if type in 'BD':
+		if '@' in symbol:
+			versionedDataSymbolsByName[symbol] = address
+		else:
+			dataSymbolsByAddress[address] = symbol
+	else:
+		if '@' in symbol:
+			versionedFunctionSymbolsByName[symbol] = address
+		else:
+			functionSymbolsByAddress[address] = symbol
+
+# add data symbols
+for dataSymbol in sorted(dataSymbolsByAddress.values()):
+	print 'int %s;' % dataSymbol
+
+print
+
+# add function symbols
+for functionSymbol in sorted(functionSymbolsByAddress.values()):
+	print 'void %s() {}' % functionSymbol
+
+print
+print "#include <symbol_versioning.h>"
+print
+
+# add symbol versioning information for data symbols
+for symbol in sorted(versionedDataSymbolsByName.keys()):
+	address = versionedDataSymbolsByName[symbol]
+	targetSymbol = dataSymbolsByAddress[address]
+	(symbolName, unused, versionTag) = symbol.partition('LIBROOT_')
+	print 'DEFINE_LIBROOT_KERNEL_SYMBOL_VERSION("%s", "%s", "%s");'	\
+		% (targetSymbol, symbolName, versionTag)
+
+# add symbol versioning information for function symbols
+for symbol in sorted(versionedFunctionSymbolsByName.keys()):
+	address = versionedFunctionSymbolsByName[symbol]
+	targetSymbol = functionSymbolsByAddress[address]
+	(symbolName, unused, versionTag) = symbol.partition('LIBROOT_')
+	print 'DEFINE_LIBROOT_KERNEL_SYMBOL_VERSION("%s", "%s", "%s");'	\
+		% (targetSymbol, symbolName, versionTag)

src/system/libroot/stubbed/libroot_stubs.c.readme

@@ -0,0 +1,19 @@
+The source file libroot_stubs.c contains empty stubs for all symbols exported by
+libroot.so, including definitions of all versioned symbols.
+
+From libroot_stubs.c, <stubbed>libroot.so can be built, which is a stubbed
+version of libroot.so (i.e. without any code). This stubbed library is used
+during stage 0 of the bootstrap process, in order to build the gcc-syslibs
+(libgcc, libsupc++ and libstdc++).
+
+The python script generate_stubs.py can be used to regenerate libroot_stubs.c
+from a built version of (the real) libroot.so. This may be necessary when new
+symbols have been added to libroot.so.
+
+The command for regenerating libroot_stubs.c is this:
+
+	nm <path-to-libroot.so> | generate_stubs.py >libroot.stubs.c
+
+There is a separate version of the stubs file for the legacy compiler (gcc2),
+which uses a different symbol mangling format and contains the symbols for
+libgcc, too.