IAR: Add post-processing step in C-STAT outputs

Harmonize IAR C-STAT headers between the first-time analysis
and subsequent builds, which uses cached results.

It also removes spurious relative paths such as `"../` and
`..\` that might appear after a new line followed by a double quote.
Effectively this will display paths relative to CMAKE_SOURCE_DIR,
similarly to the IDE, which display paths relative to $PROJ_DIR$.

Update the IAR tests to match the new C-STAT outputs.

Source/cmcmd.cxx

@@ -654,13 +654,50 @@ int HandleIcstat(std::string const& runCmd, std::string const& sourceFile,
   // Run the IAR C-STAT command line. Capture its output.
   if (!cmSystemTools::RunSingleCommand(icstat_cmd, &stdOut, &stdErr, &ret,
                                        nullptr, cmSystemTools::OUTPUT_NONE)) {
-    std::cerr << "Error running '" << icstat_cmd[0] << "': " << stdOut << '\n';
+    std::cerr << "C-STAT: Error running '" << icstat_cmd[0] << "': " << stdOut
+              << '\n';
     return 1;
   }
+
+  // Post-process successful output for consistent messaging and path cleanup.
   if (ret == 0) {
-    std::cerr << "Warning: C-STAT static analysis reported diagnostics:\n";
-  } else {
-    std::cerr << "Error: C-STAT static analysis reported failure:\n";
+    // Harmonize IAR C-STAT headers between the first-time analysis
+    // and subsequent builds that use cached results.
+    std::cerr << "C-STAT: ";
+    if (stdOut.find("Analyzing") == std::string::npos) {
+      std::string prepend;
+      prepend =
+        cmStrCat("Analyzing ", cmSystemTools::GetFilenameName(sourceFile),
+                 " (cached)\n");
+      stdOut.insert(0, prepend);
+    }
+
+    // Single-pass removal of consecutive spurious relative paths,
+    // `"../` or `"..\`, that might appear after a newline followed by
+    // an opening quote, effectively displaying paths relative to
+    // CMAKE_SOURCE_DIR.
+    // Example: `\n"../../../src/file.c` -> `\n"src/file.c`
+    std::string cleaned;
+    size_t const n = stdOut.size();
+    cleaned.reserve(n);
+    size_t pos = 0;
+    while (pos < n) {
+      if (pos + 1 < n && stdOut[pos] == '\n' && stdOut[pos + 1] == '"') {
+        cleaned += "\n\"";
+        pos += 2; // skip `\n"`
+
+        while (pos + 2 < n && stdOut[pos] == '.' && stdOut[pos + 1] == '.' &&
+               (stdOut[pos + 2] == '/' || stdOut[pos + 2] == '\\')) {
+          pos += 3; // skip `../` or `..\`
+        }
+      } else {
+        cleaned += stdOut[pos];
+        ++pos;
+      }
+    }
+    stdOut.swap(cleaned);
+  } else if (ret != 0) {
+    std::cerr << "C-STAT ";
   }
   std::cerr << stdOut;
   std::cerr << stdErr;

Tests/RunCMake/IAR/iar-c-bad-build-stdout.txt

@@ -1,3 +1,3 @@
-Error: C-STAT static analysis reported failure:
-stdout from bad command line arg '-bad'
-stderr from bad command line arg '-bad'
+C-STAT Command line error: Unexpected command line arguments:
+            -bad
+            -bad

Tests/RunCMake/IAR/iar-c-build-stdout.txt

@@ -1,2 +1 @@
-Warning: C-STAT static analysis reported diagnostics.*C-STAT analyze source: [^
-]*module\.c.*Severity
+C-STAT: Analyzing module.c.*Severity

Tests/RunCMake/IAR/iar-cxx-bad-build-stdout.txt

@@ -1,3 +1,3 @@
-Error: C-STAT static analysis reported failure:
-stdout from bad command line arg '-bad'
-stderr from bad command line arg '-bad'
+C-STAT Command line error: Unexpected command line arguments:
+            -bad
+            -bad

Tests/RunCMake/IAR/iar-cxx-build-stdout.txt

@@ -1,2 +1 @@
-Warning: C-STAT static analysis reported diagnostics.*C-STAT analyze source: [^
-]*module\.cxx.*Severity
+C-STAT: Analyzing module.cxx.*Severity

Tests/RunCMake/pseudo_icstat.c

@@ -2,6 +2,21 @@
 #include <stdlib.h>
 #include <string.h>
 
+char const* get_filename(char const* path)
+{
+  // Find the last occurrence of '/'
+  char const* last_slash = strrchr(path, '/');
+
+  // If not found, try finding the last occurrence of '\'
+  if (!last_slash) {
+    last_slash = strrchr(path, '\\');
+  }
+
+  // If a separator was found, return the character after it
+  // Otherwise, return the original path (no directory component)
+  return last_slash ? last_slash + 1 : path;
+}
+
 int main(int argc, char* argv[])
 {
   int i;
@@ -9,15 +24,18 @@ int main(int argc, char* argv[])
   char const* source = "";
   for (i = 1; i < argc; ++i) {
     if (strcmp(argv[i], "-bad") == 0) {
-      fprintf(stdout, "stdout from bad command line arg '-bad'\n");
-      fprintf(stderr, "stderr from bad command line arg '-bad'\n");
+      fprintf(
+        stdout,
+        "C-STAT Command line error: Unexpected command line arguments:\n");
+      fprintf(stdout, "            -bad\n");
+      fprintf(stderr, "            -bad\n");
       return 1;
     }
-    if (strcmp(argv[i], "analyze") == 0 && i + 1 < argc) {
-      source = argv[++i];
+    if (strcmp(argv[i], "--silent") == 0 && (i + 1) < argc) {
+      source = get_filename(argv[++i]);
     }
   }
-  fprintf(stderr, "C-STAT analyze source: %s\n", source);
+  fprintf(stderr, "C-STAT: Analyzing %s\n", source);
   fprintf(stderr,
           "\"foo/bar.c\",2 Severity-High[SPC-uninit-var-some]:"
           "Variable `i' may be uninitialized.\n\n");