Rely on compiler intrinsics to identify regex engine. (#555)

Having the copts set on a per-target level can lead to ODR violations
in some cases. Avoid this by ensuring the regex engine is picked
through compiler intrinsics in the header directly.

BUILD.bazel

@@ -1,7 +1,5 @@
 licenses(["notice"])
 
-load("//bazel:have_regex.bzl", "have_regex_copts")
-
 cc_library(
     name = "benchmark",
     srcs = glob([
@@ -9,7 +7,6 @@ cc_library(
         "src/*.h",
     ]),
     hdrs = ["include/benchmark/benchmark.h"],
-    copts = have_regex_copts(),
     strip_include_prefix = "include",
     visibility = ["//visibility:public"],
 )

bazel/BUILD

@@ -1,16 +0,0 @@
-package(default_visibility = ["//:__subpackages__"])
-
-config_setting(
-    name = "have_std_regex",
-    values = {"define": "google_benchmark.have_regex=std"},
-)
-
-config_setting(
-    name = "have_posix_regex",
-    values = {"define": "google_benchmark.have_regex=posix"},
-)
-
-config_setting(
-    name = "have_gnu_posix_regex",
-    values = {"define": "google_benchmark.have_regex=gnu_posix"},
-)

bazel/have_regex.bzl

@@ -1,7 +0,0 @@
-def have_regex_copts():
-  return select({
-      "//bazel:have_std_regex": ["-DHAVE_STD_REGEX"],
-      "//bazel:have_posix_regex": ["-DHAVE_POSIX_REGEX"],
-      "//bazel:have_gnu_posix_regex": ["-DHAVE_GNU_POSIX_REGEX"],
-      "//conditions:default": ["-DHAVE_STD_REGEX"],
-  })

src/internal_macros.h

@@ -39,6 +39,7 @@
 #elif defined(_WIN32)
   #define BENCHMARK_OS_WINDOWS 1
 #elif defined(__APPLE__)
+  #define BENCHMARK_OS_APPLE 1
   #include "TargetConditionals.h"
   #if defined(TARGET_OS_MAC)
     #define BENCHMARK_OS_MACOSX 1

src/re.h

@@ -17,9 +17,21 @@
 
 #include "internal_macros.h"
 
+#if !defined(HAVE_STD_REGEX) && \
+    !defined(HAVE_GNU_POSIX_REGEX) && \
+    !defined(HAVE_POSIX_REGEX)
+  // No explicit regex selection; detect based on builtin hints.
+  #if defined(BENCHMARK_OS_LINUX) || defined(BENCHMARK_OS_APPLE)
+    #define HAVE_POSIX_REGEX 1
+  #elif __cplusplus >= 199711L
+    #define HAVE_STD_REGEX 1
+  #endif
+#endif
+
 // Prefer C regex libraries when compiling w/o exceptions so that we can
 // correctly report errors.
-#if defined(BENCHMARK_HAS_NO_EXCEPTIONS) && defined(HAVE_STD_REGEX) && \
+#if defined(BENCHMARK_HAS_NO_EXCEPTIONS) && \
+    defined(BENCHMARK_HAVE_STD_REGEX) && \
     (defined(HAVE_GNU_POSIX_REGEX) || defined(HAVE_POSIX_REGEX))
   #undef HAVE_STD_REGEX
 #endif

test/BUILD

@@ -1,5 +1,3 @@
-load("//bazel:have_regex.bzl", "have_regex_copts")
-
 NEEDS_GTEST_MAIN = [
     "statistics_test.cc",
 ]
@@ -8,7 +6,7 @@ TEST_COPTS = [
     "-pedantic",
     "-pedantic-errors",
     "-std=c++11",
-] + have_regex_copts()
+]
 
 TEST_ARGS = ["--benchmark_min_time=0.01"]