meson: match libmali SONAME to prebuilt library version

Prebuilts with SONAME libmali.so.0 (e.g. g29p1) caused dh_shlibdeps
to pull in an unrelated package as a provider of libmali.so.1 during
parallel debuild, since the dummy was always built with version 1.9.0.

Detect the major version from the prebuilt SONAME and use it for the
dummy library so wrappers link against the correct libmali.so.N.

Author: HeyMeco

meson.build

@@ -198,12 +198,24 @@ map = {
 dummy_source = join_paths(meson.current_build_dir(), 'dummy.c')
 run_command('touch', dummy_source, check : false)
 
+# Detect the SONAME major version from the prebuilt library so that the dummy
+# and all wrapper libraries link against the same libmali.so.N as the prebuilt.
+# Without this, a prebuilt with SONAME libmali.so.0 would cause dh_shlibdeps to
+# look for a provider of libmali.so.1 (the meson default) outside the package.
+_soname_ver = run_command('sh', '-c',
+  'readelf -d "' + default_lib + '" 2>/dev/null | ' +
+  'sed -n \'s/.*SONAME.*\\[libmali\\.so\\.\\([0-9]*\\)\\].*/\\1/p\'',
+  check : false).stdout().strip()
+_ver_parts = mali_version.split('.')
+mali_lib_version = (_soname_ver != '' ? _soname_ver : _ver_parts[0]) + \
+  '.' + _ver_parts[1] + '.' + _ver_parts[2]
+
 # Create a dummy library which will be replaced by the prebuilt mali library
 libmali = shared_library(
   'mali',
   dummy_source,
   install : true,
-  version : mali_version)
+  version : mali_lib_version)
 
 libhook = []
 if build_hook