Add libtree 3.0.0-rc5 (#4062)

* Add libtree 3.0.0-rc5

* [libtree] Minor simplifications

Co-authored-by: Mosè Giordano <giordano@users.noreply.github.com>

L/libtree/build_tarballs.jl

@@ -0,0 +1,27 @@
+# Note that this script can accept some limited command-line arguments, run
+# `julia build_tarballs.jl --help` to see a usage message.
+using BinaryBuilder, Pkg
+
+name = "libtree"
+version = v"3.0.0"
+
+sources = [
+    ArchiveSource("https://github.com/haampie/libtree/archive/refs/tags/v3.0.0-rc5.tar.gz", "37be3c17a3d646c4e7814c2d642e71060c4193c1426d7725641939614c984a1d")
+]
+
+script = raw"""
+cd $WORKSPACE/srcdir/libtree-*/
+make CFLAGS="-Os -Wall -ffunction-sections -fdata-sections" LDFLAGS="-Wl,-s -Wl,--gc-sections -static" "PREFIX=$prefix" install
+"""
+
+# Build only on platforms where ELF objects are usually used.
+platforms = filter!(p -> Sys.islinux(p) || Sys.isfreebsd(p), supported_platforms(; experimental=true))
+
+products = [
+    ExecutableProduct("libtree", :libtree)
+]
+
+dependencies = Dependency[]
+
+# Note: binutils 2.24 has issues with -s and --gc-sections, so use GCC 5 which comes wth a later binutils.
+build_tarballs(ARGS, name, version, sources, script, platforms, products, dependencies; julia_compat="1.6", preferred_gcc_version = v"5")