Fix missing closing parentheses under GL_DEBUG

[kleisauke]

No description provided.

[kleisauke]

Context: #27503 (comment).

[sbc100]

Is there a test that we can add GL_DEBUG to catch this?

[sbc100]

lgtm w/test

[kleisauke]

Added a regression test in commit b1e1b9b that previously failed with:

Details

$ ./test/runner browser.test_webgl_preprocessor_variables*
Running 4 tests
Using 2 parallel test processes
...
======================================================================
FAIL: test_webgl_preprocessor_variables_webgl2_extensions (test_browser.browser.test_webgl_preprocessor_variables_webgl2_extensions)
----------------------------------------------------------------------
...

Stdout:

error: /home/kleisauke/emscripten/src/lib/libwebgl.js: failure to execute JS library "/home/kleisauke/emscripten/src/lib/libwebgl.js":
error: /home/kleisauke/emscripten/src/lib/libwebgl.js: use -sVERBOSE to save preprocessed JS
Internal compiler error JS compiler
Please create a bug report at https://github.com/emscripten-core/emscripten/issues/
with a log of the build and the input files used to run. Exception message: "/home/kleisauke/emscripten/src/lib/libwebgl.preprocessed.js:1787
    dbg(`Shader source after preprocessing: ${source}`;
                                                    ^^

SyntaxError: missing ) after argument list
...

======================================================================
FAIL: test_webgl_preprocessor_variables_webgl1_extensions (test_browser.browser.test_webgl_preprocessor_variables_webgl1_extensions)
----------------------------------------------------------------------
...

Stdout:

error: /home/kleisauke/emscripten/src/lib/libwebgl.js: failure to execute JS library "/home/kleisauke/emscripten/src/lib/libwebgl.js":
error: /home/kleisauke/emscripten/src/lib/libwebgl.js: use -sVERBOSE to save preprocessed JS
Internal compiler error JS compiler
Please create a bug report at https://github.com/emscripten-core/emscripten/issues/
with a log of the build and the input files used to run. Exception message: "/home/kleisauke/emscripten/src/lib/libwebgl.preprocessed.js:1570
    dbg(`Shader source after preprocessing: ${source}`;
                                                    ^^

SyntaxError: missing ) after argument list
...

----------------------------------------------------------------------
Ran 4 tests in 1.916s

FAILED (failures=2)
Total core time: 2.622s. Wallclock time: 1.916s. Parallelization: 1.37x.