Add support for libc++ implementation of C++ std::regex

* bench/Cargo.toml: add `libcxx` feature
* bench/build.rs: link against `libc++` when `libcxx` feature is specified with `re-stdcpp` feature. The `cc::Build::cpp_set_stdlib("c++")` method is not used because GCC does not support the `-stdlib` flag.
* bench/run: add `stdcpp-libcxx` option for benchmarking `libc++` `std::regex` implementation.

This requires the user to specify the compiler `CXX` and compiler flags `CXXFLAGS` necessary for compiling with `libc++`[1].

[1] https://libcxx.llvm.org/docs/UsingLibcxx.html

Author: mkrupcale

bench/Cargo.toml

@@ -48,6 +48,7 @@ re-pcre2 = []
 re-onig = ["onig"]
 re-stdcpp = []
 re-re2 = []
+libcxx = []
 re-dphobos = []
 re-dphobos-dmd = ["re-dphobos"]
 re-dphobos-dmd-ct = ["re-dphobos-dmd"]

bench/build.rs

@@ -20,10 +20,20 @@ fn main() {
     }
     if env::var("CARGO_FEATURE_RE_STDCPP").is_ok() {
         // stdcpp is a C++ library, so we need to compile our shim layer.
-        cc::Build::new()
-            .cpp(true)
-            .file("src/ffi/stdcpp.cpp")
-            .compile("libcstdcpp.a");
+        if !env::var("CARGO_FEATURE_LIBCXX").is_ok() {
+            // use default stdlib
+            cc::Build::new()
+                .cpp(true)
+                .file("src/ffi/stdcpp.cpp")
+                .compile("libcstdcpp.a");
+        } else {
+            // use libc++ stdlib
+            cc::Build::new()
+                .cpp(true)
+                .file("src/ffi/stdcpp.cpp")
+                .cpp_link_stdlib("c++")
+                .compile("libcstdcpp.a");
+        }
     }
     if env::var("CARGO_FEATURE_RE_RE2").is_ok() {
         // RE2 is a C++ library, so we need to compile our shim layer.

bench/run

@@ -1,7 +1,7 @@
 #!/bin/bash
 
 usage() {
-  echo "Usage: $(basename $0) [dphobos-dmd | dphobos-ldc | dphobos-dmd-ct | dphobos-ldc-ct | rust | rust-bytes | pcre1 | pcre2 | stdcpp | re2 | onig | tcl ]" >&2
+  echo "Usage: $(basename $0) [dphobos-dmd | dphobos-ldc | dphobos-dmd-ct | dphobos-ldc-ct | rust | rust-bytes | pcre1 | pcre2 | stdcpp | stdcpp-libcxx | re2 | onig | tcl ]" >&2
   exit 1
 }
 
@@ -33,6 +33,9 @@ case $which in
   stdcpp)
     exec cargo bench --bench bench --features re-stdcpp "$@"
     ;;
+  stdcpp-libcxx)
+    exec cargo bench --bench bench --features 're-stdcpp libcxx' "$@"
+    ;;
   re2)
     exec cargo bench --bench bench --features re-re2 "$@"
     ;;