Add bootstrap mode and add necessary conditionals for building rebar with a self-hosted rebar

Rebar is built with rebar, which makes getting the initial bootstrap
completed rather interesting. Additionally, erlang-rebar requires
erlang-getopt, but erlang-rebar can't be built without erlang-getopt
already available in the repo mock is using because of the patch which
removes the vendored version. This commit adds a variable which uses the
bundled getopt in order to bootstrap.

erlang-rebar.spec

@@ -4,6 +4,13 @@
 %global git_tag ebb474b
 %global patchnumber 0
 
+# Set this to true when starting a rebuild of the whole erlang stack. There's
+# a cyclical dependency between erlang-rebar and erlang-getopt so this package
+# (rebar) needs to get built first in bootstrap mode.
+%global need_bootstrap_set 0
+
+%{!?need_bootstrap: %global need_bootstrap  %{need_bootstrap_set}}
+
 
 Name:		erlang-%{realname}
 Version:	2.1.0
@@ -19,8 +26,13 @@ Source1:	rebar.escript
 Patch1:		rebar-0001-Don-t-load-templates-from-the-bundle.patch
 # Fedora/EPEL-specific
 Patch2:		rebar-0002-Remove-bundled-mustache.patch
+
+# The bundled getopt is necessary to do the initial bootstrap since
+# erlang-getopt requires erlang-rebar to build and vice versa.
+%if 0%{?need_bootstrap} < 1
 # Fedora/EPEL-specific
 Patch3:		rebar-0003-Remove-bundled-getopt.patch
+%endif
 # Backported from upstream
 Patch4:		rebar-0004-Be-sure-to-filter-empty-sources-h-t-to-Tuncer-and-Jo.patch
 # Will be proposed for inclusion
@@ -35,7 +47,13 @@ Patch8:		rebar-0008-Remove-abnfc-compiler-support-n-a-in-Fedora-EPEL.patch
 Patch9:		rebar-0009-Adjust-app-version.patch
 # Backported from upstream
 Patch10:	rebar-0010-Fix-default-DTL-compilation-when-no-erlydtl_opts-are.patch
+
+%if 0%{?need_bootstrap} < 1
 BuildRequires:	erlang-rebar
+%else
+BuildRequires: erlang
+%endif
+
 # FIXME wip
 #Requires:	erlang-abnfc%{?_isa}
 Requires:	erlang-asn1%{?_isa}
@@ -77,7 +95,9 @@ Erlang Build Tools.
 %setup -q -n %{upstream}-%{realname}-%{git_tag}
 %patch1 -p1 -b .dont_load_templates
 %patch2 -p1 -b .remove_bundled_mustache
+%if 0%{?need_bootstrap} < 1
 %patch3 -p1 -b .remove_bundled_getopt
+%endif
 %patch4 -p1 -b .dont_try_building_so
 %patch5 -p1 -b .allow_discarding_ports
 %patch6 -p1 -b .use_locally_installed
@@ -88,7 +108,12 @@ Erlang Build Tools.
 
 
 %build
+%if 0%{?need_bootstrap} < 1
 rebar compile -v
+%else
+./bootstrap
+./rebar compile -v
+%endif
 
 
 %install