We provided two 5.1.2alpha symbols (lzma_stream_encoder_mt and
lzma_stream_encoder_mt_memusage) before we updated to xz-5.2.2-1 in RHEL7.3.

Those symbols did not change ABI in 5.2.2 so it should be safe to provide
(except for 5.0 and 5.2 symbols) also the two 5.1.2alpha symbols and
use 5.1.2alpha symbol version as parent for 5.2.

For better reasoning look at container.h in 5.1.2alpha -- those two symbols
were for testing purposes only, and thus not considered to be API/ABI.

diff --git a/src/liblzma/liblzma.map b/src/liblzma/liblzma.map
index f53a4ea..9c3002a 100644
--- a/src/liblzma/liblzma.map
+++ b/src/liblzma/liblzma.map
@@ -95,7 +95,13 @@ global:
 	lzma_vli_size;
 };
 
-XZ_5.2 {
+XZ_5.1.2alpha {
+global:
+	lzma_stream_encoder_mt;
+	lzma_stream_encoder_mt_memusage;
+} XZ_5.0;
+
+XZ_5.2.2 {
 global:
 	lzma_block_uncomp_encode;
 	lzma_cputhreads;
@@ -105,4 +111,4 @@ global:
 
 local:
 	*;
-} XZ_5.0;
+} XZ_5.1.2alpha;