Add parentheses to appease -Wstring-concatenation

Bug: 1114873
Change-Id: I1d9fa0fc6577cd49db8d1b58f63cd72646a88531
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2385979
Auto-Submit: Arthur Eubanks <aeubanks@google.com>
Reviewed-by: Nico Weber <thakis@chromium.org>
Reviewed-by: Victor Miura <vmiura@chromium.org>
Commit-Queue: Victor Miura <vmiura@chromium.org>
Cr-Commit-Position: refs/heads/master@{#803935}

gpu/command_buffer/tests/lpm/gl_lpm_fuzzer.cc

@@ -116,8 +116,8 @@ const char* acceptable_errors[] = {
     // Uniform, const, input can't be modified
     "can't modify a",
     "global variable initializers must be constant expressions",
-    "must explicitly specify all locations when using multiple fragment "
-    "outputs",
+    ("must explicitly specify all locations when using multiple fragment "
+     "outputs"),
 };
 
 // Filter errors which we don't think interfere with fuzzing everything.