From https://gitlab.alpinelinux.org/alpine/aports/-/merge_requests/35711#note_243863
_GNU_SOURCE is needed for cpu_set_t, and affinity disable is needed to work around lack of pthread_attr_setaffinity_np
--- a/libraries/lzma/CMakeLists.txt
+++ b/libraries/lzma/CMakeLists.txt
@@ -2,7 +2,7 @@
 
 make_release_only()
 
-set( CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -D_7ZIP_PPMD_SUPPPORT" )
+set( CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -D_GNU_SOURCE -D_7ZIP_PPMD_SUPPPORT -D _7ZIP_AFFINITY_DISABLE" )
 
 find_package(Threads)