Fix RHEL/ELN builds

The eln macro requires ELN SIG approval, and there is no need to differ
from RHEL here.  More importantly, we don't want the dynamic
buildrequires in ELN either.

RHEL/ELN cargo macros do not support -f, so import the RHEL/c9s patch
which adds rdcore to the default features.

While we're at it, use the RHEL %%cargo_prep -V to handle vendoring
rather than manually modifing the cargo config.

enable-rdcore.patch

@@ -0,0 +1,11 @@
+diff -ur a/Cargo.toml b/Cargo.toml
+--- a/Cargo.toml	1969-12-31 19:00:01.000000000 -0500
++++ b/Cargo.toml	2023-03-14 07:57:14.025021766 -0400
+@@ -195,6 +195,7 @@
+ 
+ [features]
+ docgen = ["dep:clap_mangen"]
++default = ["rdcore"]
+ rdcore = []
+ 
+ [target."cfg(target_arch = \"s390x\")".dependencies.mbrman]

rust-coreos-installer.spec

@@ -23,8 +23,12 @@ Source0:        https://crates.io/api/v1/crates/%{crate}/%{version}/download#/%{
 Source1:        https://github.com/coreos/%{crate}/releases/download/v%{version}/%{crate}-%{version}-vendor.tar.gz
 Source2:        https://github.com/coreos/coreos-installer-dracut/archive/%{dracutcommit}/coreos-installer-dracut-%{dracutshortcommit}.tar.gz
 
+## RHEL specific patches
+# enable rdcore in default feature set (RHEL macros do not take -f)
+Patch1000:      enable-rdcore.patch
+
 ExclusiveArch:  %{rust_arches}
-%if 0%{?rhel} && !0%{?eln}
+%if 0%{?rhel}
 BuildRequires:  rust-toolset
 BuildRequires:  openssl-devel
 # To ensure we're not bundling system libraries
@@ -79,17 +83,10 @@ Obsoletes:      coreos-installer-dracut < 0.0.1
 %description -n %{crate} %{_description}
 
 %prep
-%autosetup -n %{crate}-%{version} -p1 -a 2
-%if 0%{?rhel} && !0%{?eln}
-tar xvf %{SOURCE1}
-mkdir -p .cargo
-cat >.cargo/config << EOF
-[source.crates-io]
-replace-with = "vendored-sources"
-
-[source.vendored-sources]
-directory = "vendor"
-EOF
+%autosetup -n %{crate}-%{version} -N -a 2
+%autopatch -p1 %{?!rhel:-M 999}
+%if 0%{?rhel}
+%cargo_prep -V 1
 %else
 %cargo_prep
 %endif
@@ -97,20 +94,20 @@ EOF
 # https://bugzilla.redhat.com/show_bug.cgi?id=1883457
 sed -i 's/"-Ccodegen-units=1",//' .cargo/config
 
-%if !0%{?rhel} || 0%{?eln}
+%if !0%{?rhel}
 %generate_buildrequires
 %cargo_generate_buildrequires -f rdcore
 %endif
 
 %build
-%if 0%{?rhel} && !0%{?eln}
+%if 0%{?rhel}
 %cargo_build
 %else
 %cargo_build -f rdcore
 %endif
 
 %install
-%if 0%{?rhel} && !0%{?eln}
+%if 0%{?rhel}
 %make_install RELEASE=1
 %else
 %cargo_install -f rdcore
@@ -172,7 +169,7 @@ from the initramfs in IoT/Edge and is supported by the community.
 
 %if %{with check}
 %check
-%if 0%{?rhel} && !0%{?eln}
+%if 0%{?rhel}
 %cargo_test
 %else
 %cargo_test -f rdcore