Fix Wunused-but-set-variable warnings

Change-Id: I0e093fd35b11e9a765ef9c09f3b6346086ff66bf
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/435983
Reviewed-by: Jim Van Verth <jvanverth@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
diff --git a/src/sksl/SkSLDehydrator.cpp b/src/sksl/SkSLDehydrator.cpp
index ab55f3f..522571c 100644
--- a/src/sksl/SkSLDehydrator.cpp
+++ b/src/sksl/SkSLDehydrator.cpp
@@ -239,12 +239,12 @@
         ordered.insert({name, symbol});
     });
     for (std::pair<skstd::string_view, const Symbol*> p : ordered) {
-        bool found = false;
+        SkDEBUGCODE(bool found = false;)
         for (size_t i = 0; i < symbols.fOwnedSymbols.size(); ++i) {
             if (symbols.fOwnedSymbols[i].get() == p.second) {
                 fCommandBreaks.add(fBody.bytesWritten());
                 this->writeU16(i);
-                found = true;
+                SkDEBUGCODE(found = true;)
                 break;
             }
         }