Dynamically load compression libraries

TODO

@@ -1400,8 +1400,8 @@ Features:
     - kmod-libs (only when called from PID 1)
     - libblkid (only in RootImage= handling in PID 1, but not elsewhere)
     - libpam (only when called from PID 1)
-    - bzip2, xz, lz4 (always — gzip and zstd should probably stay static deps the way they are,
-      since they are so basic and our defaults)
+    - bzip2 (always — gzip should probably stay static dep the way it is,
+      since it's so basic and our defaults)
 
 * seccomp: maybe use seccomp_merge() to merge our filters per-arch if we can.
   Apparently kernel performance is much better with fewer larger seccomp

meson.build

@@ -1371,16 +1371,19 @@ conf.set10('HAVE_BZIP2', libbzip2.found())
 libxz = dependency('liblzma',
                    required : get_option('xz'))
 conf.set10('HAVE_XZ', libxz.found())
+libxz_cflags = libxz.partial_dependency(includes: true, compile_args: true)
 
 liblz4 = dependency('liblz4',
                     version : '>= 1.3.0',
                     required : get_option('lz4'))
 conf.set10('HAVE_LZ4', liblz4.found())
+liblz4_cflags = liblz4.partial_dependency(includes: true, compile_args: true)
 
 libzstd = dependency('libzstd',
                      version : '>= 1.4.0',
                      required : get_option('zstd'))
 conf.set10('HAVE_ZSTD', libzstd.found())
+libzstd_cflags = libzstd.partial_dependency(includes: true, compile_args: true)
 
 conf.set10('HAVE_COMPRESSION', libxz.found() or liblz4.found() or libzstd.found())
 
@@ -1951,8 +1954,7 @@ libsystemd = shared_library(
         link_args : ['-shared',
                      '-Wl,--version-script=' + libsystemd_sym_path],
         link_with : [libbasic,
-                     libbasic_gcrypt,
-                     libbasic_compress],
+                     libbasic_gcrypt],
         link_whole : [libsystemd_static],
         dependencies : [librt,
                         threads,
@@ -1969,7 +1971,6 @@ install_libsystemd_static = static_library(
         libsystemd_sources,
         basic_sources,
         basic_gcrypt_sources,
-        basic_compress_sources,
         fundamental_sources,
         include_directories : libsystemd_includes,
         build_by_default : static_libsystemd != 'false',
@@ -1981,12 +1982,12 @@ install_libsystemd_static = static_library(
                         libcap,
                         libdl,
                         libgcrypt,
-                        liblz4,
+                        liblz4_cflags,
                         libmount,
                         libopenssl,
                         librt,
-                        libxz,
-                        libzstd,
+                        libxz_cflags,
+                        libzstd_cflags,
                         threads,
                         userspace],
         c_args : libsystemd_c_args + (static_libsystemd_pic ? [] : ['-fno-PIC']))