libllvm-size: Add compat package support

Detect libLLVM path using llvm-config to make the script
reusable with compat packages.

tests/libllvm-size/main.fmf

@@ -2,5 +2,5 @@ summary: Check that libLLVM.so has been properly stripped
 tier: 1
 duration: 1m
 
-environment:
-  LIBLLVM_PATH: /usr/lib64/libLLVM.so
+require+:
+  - llvm-devel

tests/libllvm-size/test.sh

@@ -1,5 +1,10 @@
 #!/bin/bash -eux
 
+# Retrieve libLLVM path if not set via environment variable. This is necessary
+# to make the test flexible enough to use it with both compat and unversioned
+# packages.
+LIBLLVM_PATH=${LIBLLVM_PATH:-"$(llvm-config --libfiles)"}
+
 # There is a bug in the build process when it runs out of disk space
 # while stripping binaries, which causes the strip to fail, but does
 # not fail the build.  This results in a libLLVM.so that is over 2GB