[source] gcc: fix build error with macOS + Xcode 9

[LEDE Commits]

nbd pushed a commit to source.git, branch master:
https://git.lede-project.org/07a99a83f21ac6d23ec26affdd032424aff6a6e9

commit 07a99a83f21ac6d23ec26affdd032424aff6a6e9
Author: Felix Fietkau <nbd at nbd.name>
AuthorDate: Thu Oct 5 19:46:48 2017 +0200

    gcc: fix build error with macOS + Xcode 9
    
    Signed-off-by: Felix Fietkau <nbd at nbd.name>
---
 .../gcc/patches/5.4.0/030-macos-header-fix-backport.patch      | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/toolchain/gcc/patches/5.4.0/030-macos-header-fix-backport.patch b/toolchain/gcc/patches/5.4.0/030-macos-header-fix-backport.patch
new file mode 100644
index 0000000..37c774e
--- /dev/null
+++ b/toolchain/gcc/patches/5.4.0/030-macos-header-fix-backport.patch
@@ -0,0 +1,10 @@
+--- a/gcc/system.h
++++ b/gcc/system.h
+@@ -216,6 +216,7 @@ extern int errno;
+ 
+ #ifdef __cplusplus
+ # include <algorithm>
++# include <map>
+ # include <cstring>
+ # include <utility>
+ #endif