Add DevkitPPC support

DevkitPPC does not support unix sockets natively, meaning that bindings
to these functions was removed for powerpc targets with "nintendo" as
vendor.

Suggested target json files:

Nintendo Gamecube:
```
{
  "arch": "powerpc",
  "data-layout": "E-m:e-p:32:32-i64:64-n32",
  "dynamic-linking": false,
  "env": "newlib",
  "executables": true,
  "has-elf-tls": false,
  "has-rpath": true,
  "linker-flavor": "gcc",
  "llvm-target": "powerpc-eabi",
  "max-atomic-width": 32,
  "os": "dolphin",
  "target-c-int-width": "32",
  "target-endian": "big",
  "target-family": "unix",
  "target-mcount": "_mcount",
  "target-pointer-width": "32",
  "vendor": "nintendo"
}
```

Nintendo Wii:
```
{
  "arch": "powerpc",
  "data-layout": "E-m:e-p:32:32-i64:64-n32",
  "dynamic-linking": false,
  "env": "newlib",
  "executables": true,
  "has-elf-tls": false,
  "has-rpath": true,
  "linker-flavor": "gcc",
  "llvm-target": "powerpc-eabi",
  "max-atomic-width": 32,
  "os": "revolution",
  "target-c-int-width": "32",
  "target-endian": "big",
  "target-family": "unix",
  "target-mcount": "_mcount",
  "target-pointer-width": "32",
  "vendor": "nintendo"
}
```

1 files changed, 2 insertions, 1 deletions

diff --git a/build.rs b/build.rs
index f447c0ef9c..27cfb02401 100644
--- a/build.rs
+++ b/build.rs
@@ -65,9 +65,10 @@ fn main() {
         println!("cargo:rustc-cfg=libc_core_cvoid");
     }
 
-    // Rust >= 1.33 supports repr(packed(N))
+    // Rust >= 1.33 supports repr(packed(N)) and cfg(target_vendor).
     if rustc_minor_ver >= 33 || rustc_dep_of_std {
         println!("cargo:rustc-cfg=libc_packedN");
+        println!("cargo:rustc-cfg=libc_cfg_target_vendor");
     }
 
     // #[thread_local] is currently unstable