Clarify the implications of symbol_level = 1

build/config/compiler/compiler.gni

Index: build/config/compiler/compiler.gni
diff --git a/build/config/compiler/compiler.gni b/build/config/compiler/compiler.gni
index 66c65e0550ab2b788e714662c2e401bb211a3b92..403dd4fd320e37951467fadc5c3a116e92405bf5 100644
--- a/build/config/compiler/compiler.gni
+++ b/build/config/compiler/compiler.gni
@@ -15,7 +15,9 @@ declare_args() {
   # How many symbols to include in the build. This affects the performance of
   # the build since the symbols are large and dealing with them is slow.
   #   2 means regular build with symbols.
-  #   1 means minimal symbols, usually enough for backtraces only.
+  #   1 means minimal symbols, usually enough for backtraces only. Symbols with
+  # internal linkage (static functions or those in anonymous namespaces) may not
+  # appear when using this level.
   #   0 means no symbols.
   #   -1 means auto-set according to debug/release and platform.
   symbol_level = -1