fix(cmake): Fall back to version from components when git describe fails

When version.txt does not exist and git describe fails (e.g. in
release archives or environments without git), IDF_VER was set to
the raw git_describe output which resolves to "-128-NOTFOUND",
causing esp_get_idf_version() to return a garbled string.

Add a fallback that constructs the version string from the
IDF_VERSION_MAJOR, IDF_VERSION_MINOR and IDF_VERSION_PATCH
variables when git describe is not available.

Closes https://github.com/espressif/esp-idf/issues/18240

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Signed-off-by: Frantisek Hrbata <frantisek.hrbata@espressif.com>

tools/cmake/build.cmake

@@ -147,8 +147,10 @@ function(__build_get_idf_git_revision)
     if(EXISTS "${idf_path}/version.txt")
         file(STRINGS "${idf_path}/version.txt" idf_ver_t)
         set_property(DIRECTORY APPEND PROPERTY CMAKE_CONFIGURE_DEPENDS "${idf_path}/version.txt")
-    else()
+    elseif(idf_ver_git)
         set(idf_ver_t ${idf_ver_git})
+    else()
+        set(idf_ver_t "v${IDF_VERSION_MAJOR}.${IDF_VERSION_MINOR}.${IDF_VERSION_PATCH}")
     endif()
     # cut IDF_VER to required 32 characters.
     string(SUBSTRING "${idf_ver_t}" 0 31 idf_ver)