string(REGEX MATCH): Restore reporting of matches with semicolons

This was broken by refactoring in commit dab5e6ebb1 (introduce
cm::CMakeString class as helper for string() command, 2025-10-06,
v4.3.0-rc1~510^2~2).

Fixes: #27749

Source/cmCMakeString.cxx

@@ -96,7 +96,7 @@ cmList CMakeString::Match(std::string const& matchExpression,
       if (makefile) {
         makefile->StoreMatches(re);
       }
-      output = re.match();
+      output.push_back(re.match());
     }
   } else {
     unsigned optAnchor = 0;

Tests/RunCMake/string/RegexMatch.cmake

@@ -0,0 +1,15 @@
+
+cmake_policy(SET CMP0186 NEW)
+
+function(check_output name expected)
+  set(output "${${name}}")
+  if(NOT output STREQUAL expected)
+    message(FATAL_ERROR "\"string(REGEX)\" set ${name} to \"${output}\", expected \"${expected}\"")
+  endif()
+endfunction()
+
+string(REGEX MATCH ".*" out "abcd;")
+check_output(out "abcd;")
+
+string(REGEX MATCHALL "^.*" out "abcd;")
+check_output(out "abcd;")

Tests/RunCMake/string/RunCMakeTest.cmake

@@ -42,6 +42,7 @@ run_cmake(UuidMissingNameValue)
 run_cmake(UuidMissingTypeValue)
 run_cmake(UuidBadType)
 
+run_cmake(RegexMatch)
 run_cmake(RegexClear)
 run_cmake(RegexMultiMatchClear)
 run_cmake(RegexEmptyMatch)