Sync versioning schemes between Meson and CMake

Use a computed soversion of 1.

This keeps compatibility with the version in the SONAME from openSUSE
and Fedora, which fixed the botched soname in bzip2's historical
tarballs.

See this post for details:
https://people.gnome.org/~federico/blog/preparing-the-bzip2-107-release.html

CMakeLists.txt

@@ -7,6 +7,8 @@ project(bzip2
 
 # See versioning rule:
 #  http://www.gnu.org/software/libtool/manual/html_node/Updating-version-info.html
+#
+# KEEP THESE IN SYNC WITH meson.build OR STUFF WILL BREAK!
 set(LT_CURRENT  1)
 set(LT_REVISION 6)
 set(LT_AGE      0)

meson.build

@@ -27,13 +27,37 @@ endif
 
 bz_sources = ['blocksort.c', 'huffman.c', 'crctable.c', 'randtable.c', 'compress.c', 'decompress.c', 'bzlib.c']
 
+## Library versioning
+##
+## New package version:
+##   revision += 1
+##
+## New interfaces:
+##   current += 1
+##   revision = 0
+##   age += 1
+##
+## Deleted/changed interfaces:
+##   current += 1
+##   revision = 0
+##   age = 0
+##
+## KEEP THESE IN SYNC WITH CMakeLists.txt OR STUFF WILL BREAK!
+bz2_lt_current  = 1
+bz2_lt_revision = 6
+bz2_lt_age      = 0
+
+bz2_soversion   = bz2_lt_current - bz2_lt_age
+bz2_lt_version  = '@0@.@1@.@2@'.format(bz2_soversion, bz2_lt_age, bz2_lt_revision)
+
 if ['msvc', 'clang-cl', 'intel-cl'].contains(cc.get_id())
   libbzip2 = library(
     'bz2',
     bz_sources,
     c_args : c_args,
     vs_module_defs : 'libbz2.def',
-    version : meson.project_version(),
+    version : bz2_lt_version,
+    soversion : bz2_soversion,
     install : true,
   )
 else
@@ -42,7 +66,8 @@ else
     bz_sources,
     c_args : c_args,
     gnu_symbol_visibility : 'hidden',
-    version : meson.project_version(),
+    version : bz2_lt_version,
+    soversion : bz2_soversion,
     install : true,
   )
 endif