test(e2e): ldd's interpreter line is about ldd, not about the artifact

The host-library check I added a commit ago failed on CI for a dependency the
artifact does not have:

  /home/runner/.mcpp/.../xim-x-glibc/2.39/lib64/ld-linux-x86-64.so.2
      => /lib64/ld-linux-x86-64.so.2

ldd resolves the program interpreter by running the host's loader, so it
always reports the payload interpreter as resolving to the host's. That says
nothing about what the artifact loads at runtime -- the PT_INTERP assertion
above already covers the interpreter, and it passed.

A real dependency has a bare soname on the left; the interpreter line has an
absolute path. The predicate now requires the former, and is self-checked
against all three line shapes before use.

Worth stating plainly: this is a check that would have blocked correct work
while claiming a defect. That is the opposite failure from the ones this
branch has been chasing, and no less expensive.

Author: speak-agent

tests/e2e/201_gcc_no_specs_pollution.sh

@@ -92,9 +92,19 @@ echo "$out" | grep -q 'Hello' || { echo "unexpected output: $out"; exit 1; }
 #
 # Asking where each library actually came from makes the same defect visible
 # everywhere, host toolchain or not.
+# Only lines whose LEFT side is a bare soname count. ldd resolves the program
+# interpreter by running the host's loader, so it always reports the
+# interpreter as `<payload>/ld-linux-x86-64.so.2 => /lib64/ld-linux-x86-64.so.2`
+# -- a statement about ldd, not about the artifact, and a false positive that
+# failed this very check on CI. A real dependency has no slash on the left.
+host_lib_lines() {
+    ldd "$1" 2>/dev/null \
+        | grep -E '^[[:space:]]*[^/[:space:]]+ => +(/lib|/usr/lib|/lib64|/usr/lib64)/' \
+        || true
+}
+
 if command -v ldd > /dev/null 2>&1; then
-    host_libs=$(ldd "$bin" 2>/dev/null \
-                | grep -E '=> +(/lib|/usr/lib|/lib64|/usr/lib64)/' || true)
+    host_libs=$(host_lib_lines "$bin")
     if [[ -n "$host_libs" ]]; then
         echo "the artifact loads libraries from the host:"
         echo "$host_libs" | sed 's/^/  /'
@@ -147,8 +157,7 @@ EOF
 pfbin=$(find target -type f -name pf -path '*/bin/*' | head -1)
 [[ -n "$pfbin" ]] || { echo "no payload-first binary produced"; exit 1; }
 
-pf_host=$(ldd "$pfbin" 2>/dev/null \
-          | grep -E '=> +(/lib|/usr/lib|/lib64|/usr/lib64)/' || true)
+pf_host=$(host_lib_lines "$pfbin")
 if [[ -n "$pf_host" ]]; then
     echo "the payload-first artifact loads libraries from the host:"
     echo "$pf_host" | sed 's/^/  /'