builder: archs for oraclelinux-8; el-8 symlinks

(cherry picked from commit dee53cf16161a6c45560475b647de420842532ef)

builder: add el-7 alias for centos-7

(cherry picked from commit 6bd3c9bb23f5dfc385a66647ab175ec2812d6617)

diff --git a/builder-support/dockerfiles/Dockerfile.target.el-7 b/builder-support/dockerfiles/Dockerfile.target.el-7
new file mode 120000 (symlink)
index 0000000..c6fc1ef
--- /dev/null
+++ b/builder-support/dockerfiles/Dockerfile.target.el-7
@@ -0,0 +1 @@
+Dockerfile.target.centos-7
\ No newline at end of file

diff --git a/builder-support/dockerfiles/Dockerfile.target.el-8 b/builder-support/dockerfiles/Dockerfile.target.el-8
new file mode 120000 (symlink)
index 0000000..608942e
--- /dev/null
+++ b/builder-support/dockerfiles/Dockerfile.target.el-8
@@ -0,0 +1 @@
+Dockerfile.target.oraclelinux-8
\ No newline at end of file