Enable ClangTidy flag bugprone-suspicious-string-compare.

https://clang.llvm.org/extra/clang-tidy/checks/bugprone-suspicious-string-compare.html

Find suspicious usage of runtime string comparison functions.
This check is valid in C and C++.

Checks for calls with implicit comparator and proposed to
explicitly add it:

  if (strcmp(...))       // Implicitly compare to zero
  if (!strcmp(...))      // Won't warn
  if (strcmp(...) != 0)  // Won't warn

Checks that compare function results (i,e, strcmp) are compared to valid
constant. The resulting value is

  <  0    when lower than,
  >  0    when greater than,
  == 0    when equals.

A common mistake is to compare the result to 1 or -1:

  if (strcmp(...) == -1)  // Incorrect usage of the returned value.

Additionally, the check warns if the results value is implicitly cast
to a suspicious non-integer type. It’s happening when the returned
value is used in a wrong context:

  if (strcmp(...) < 0.)  // Incorrect usage of the returned value.

Change-Id: I001b88d06cc4f3eb5846103885be675f9b78e126
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/310761
Commit-Queue: John Stiles <johnstiles@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>
diff --git a/.clang-tidy b/.clang-tidy
index cb38913..178f4a5 100644
--- a/.clang-tidy
+++ b/.clang-tidy
@@ -2,6 +2,7 @@
     -*,
     bugprone-argument-comment,
     bugprone-bool-pointer-implicit-conversion,
+    bugprone-suspicious-string-compare,
     bugprone-undelegated-constructor,
     bugprone-unused-raii,
     bugprone-use-after-move,