Support for adding libraries compiled with the alternative gcc (2 vs.

4). One has to have a (fully configured) "generated" directory for the
alternative gcc and specify it using the new option
"--alternative-gcc-output-dir" when configuring the main build.
Additionally the build variable HAIKU_ADD_ALTERNATIVE_GCC_LIBS has to be
set to "1".

If that has been done, when building the image a sub-jam is invoked that
generates the alternative libs and zips them. The main-jam unzips them
into the correct directory in the image. Note that the JAM build
variable has to be set when using a jam executable not invoked by "jam".

Tested with gcc 2 NetPositive, Pe, and FireFox under gcc 4 Haiku, and
with a few of the standard gcc 4 Haiku apps under gcc 2 Haiku. Seems to
work fine so far.


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@25536 a95241bf-73f2-0310-859d-f6bbb57e9c96

build/jam/UserBuildConfig.sample

@@ -32,3 +32,6 @@
 
 # Add all available optional packages.
 #HAIKU_ADD_ALL_OPTIONAL_PACKAGES = 1 ;
+
+# Add the libraries built with the alternative gcc version.
+#HAIKU_ADD_ALTERNATIVE_GCC_LIBS = 1 ;