msg-filter: tweak kernel path fixup for z-stream releases

The original rule was able to translate:
`kernel-4.18.0-552.el8/linux-4.18.0-552.el8.x86_64/` -> `kernel-4.18.0-552.el8/`

... but it did not work for z-stream releases, where the paths are
unnecessarily inconsistent (`el8_9` on the first level vs. `el8`
on the second level):
`kernel-4.18.0-513.5.1.el8_9/linux-4.18.0-513.5.1.el8.x86_64/`

Related: https://issues.redhat.com/browse/OSH-563
Closes: csutils#171

src/lib/msg-filter.cc

@@ -66,7 +66,7 @@ struct MsgFilter::Private {
     TSubstMap fileSubsts;
 
     const std::string strKrn = "^[a-zA-Z+]+";
-    const RE reKrn = RE(strKrn);
+    const RE reKrn = RE(strKrn + /* convert el8_9 -> el8 */ "|_[0-9]+$");
     const RE reDir = RE("^([^:]*/)");
     const RE reFile = RE("[^/]+$");
     const RE rePath = RE("^(?:/builddir/build/BUILD/)?([^/]+)/(.*)(\\.[ly])?$");

tests/csdiff/CMakeLists.txt

@@ -85,5 +85,6 @@ test_csdiff(diff-misc 17-cov-parser-key-event)
 test_csdiff(diff-misc 18-cov-parser-key-event)
 test_csdiff(diff-misc 19-cov-parser-key-event)
 test_csdiff(diff-misc 21-kernel-shell-code)
+test_csdiff(diff-misc 22-kernel-zstream-path)
 
 add_subdirectory(filter-file)

tests/csdiff/diff-misc/22-kernel-zstream-path-new.err

@@ -0,0 +1,11 @@
+Error: UNINIT (CWE-457):
+kernel-4.18.0-552.el8/linux-4.18.0-552.el8.x86_64/arch/x86/crypto/chacha20_glue.c:71:2: var_decl: Declaring variable "walk" without initializer.
+kernel-4.18.0-552.el8/linux-4.18.0-552.el8.x86_64/arch/x86/crypto/chacha20_glue.c:74:2: path: Condition "__cond", taking false branch.
+kernel-4.18.0-552.el8/linux-4.18.0-552.el8.x86_64/arch/x86/crypto/chacha20_glue.c:77:2: path: Condition "req->cryptlen <= 64", taking false branch.
+kernel-4.18.0-552.el8/linux-4.18.0-552.el8.x86_64/arch/x86/crypto/chacha20_glue.c:77:2: path: Condition "!may_use_simd()", taking false branch.
+kernel-4.18.0-552.el8/linux-4.18.0-552.el8.x86_64/arch/x86/crypto/chacha20_glue.c:80:2: uninit_use_in_call: Using uninitialized value "walk.flags" when calling "skcipher_walk_virt".
+#   78|   		return crypto_chacha20_crypt(req);
+#   79|   
+#   80|-> 	err = skcipher_walk_virt(&walk, req, true);
+#   81|   
+#   82|   	crypto_chacha20_init(state, ctx, walk.iv);

tests/csdiff/diff-misc/22-kernel-zstream-path-old.err

@@ -0,0 +1,11 @@
+Error: UNINIT (CWE-457):
+kernel-4.18.0-513.5.1.el8_9/linux-4.18.0-513.5.1.el8.x86_64/arch/x86/crypto/chacha20_glue.c:71: var_decl: Declaring variable "walk" without initializer.
+kernel-4.18.0-513.5.1.el8_9/linux-4.18.0-513.5.1.el8.x86_64/arch/x86/crypto/chacha20_glue.c:74: path: Condition "__cond", taking false branch.
+kernel-4.18.0-513.5.1.el8_9/linux-4.18.0-513.5.1.el8.x86_64/arch/x86/crypto/chacha20_glue.c:77: path: Condition "req->cryptlen <= 64", taking false branch.
+kernel-4.18.0-513.5.1.el8_9/linux-4.18.0-513.5.1.el8.x86_64/arch/x86/crypto/chacha20_glue.c:77: path: Condition "!may_use_simd()", taking false branch.
+kernel-4.18.0-513.5.1.el8_9/linux-4.18.0-513.5.1.el8.x86_64/arch/x86/crypto/chacha20_glue.c:80: uninit_use_in_call: Using uninitialized value "walk.flags" when calling "skcipher_walk_virt".
+#   78|   		return crypto_chacha20_crypt(req);
+#   79|   
+#   80|-> 	err = skcipher_walk_virt(&walk, req, true);
+#   81|   
+#   82|   	crypto_chacha20_init(state, ctx, walk.iv);