[openwrt/openwrt] nettle: fix build on macos xcode 12

[LEDE Commits]

ldir pushed a commit to openwrt/openwrt.git, branch master:
https://git.openwrt.org/6429307a3d6ba4c88d477cc7a3995be314e3dd15

commit 6429307a3d6ba4c88d477cc7a3995be314e3dd15
Author: Kevin Darbyshire-Bryant <ldir at darbyshire-bryant.me.uk>
AuthorDate: Mon Nov 16 08:52:49 2020 +0000

    nettle: fix build on macos xcode 12
    
    compiler warns that exit() isn't defined so checks for build system
    compiler fail.
    
    include <stdlib.h> to define exit()
    
    Tested under macos Catalina & Big Sur
    
    Signed-off-by: Kevin Darbyshire-Bryant <ldir at darbyshire-bryant.me.uk>
---
 package/libs/nettle/patches/100-portability.patch | 34 +++++++++++++++++++++++
 1 file changed, 34 insertions(+)

diff --git a/package/libs/nettle/patches/100-portability.patch b/package/libs/nettle/patches/100-portability.patch
new file mode 100644
index 0000000000..2849e53eab
--- /dev/null
+++ b/package/libs/nettle/patches/100-portability.patch
@@ -0,0 +1,34 @@
+--- a/configure
++++ b/configure
+@@ -4635,6 +4635,7 @@ $as_echo_n "checking build system compil
+ # remove anything that might look like compiler output to our "||" expression
+ rm -f conftest* a.out b.out a.exe a_out.exe
+ cat >conftest.c <<EOF
++#include <stdlib.h>
+ int
+ main ()
+ {
+@@ -4667,6 +4668,7 @@ $as_echo_n "checking build system compil
+ # remove anything that might look like compiler output to our "||" expression
+ rm -f conftest* a.out b.out a.exe a_out.exe
+ cat >conftest.c <<EOF
++#include <stdlib.h>
+ int
+ main ()
+ {
+@@ -4703,6 +4705,7 @@ $as_echo_n "checking build system compil
+ # remove anything that might look like compiler output to our "||" expression
+ rm -f conftest* a.out b.out a.exe a_out.exe
+ cat >conftest.c <<EOF
++#include <stdlib.h>
+ int
+ main ()
+ {
+@@ -4753,6 +4756,7 @@ else
+   gmp_cv_prog_exeext_for_build="$EXEEXT"
+ else
+   cat >conftest.c <<EOF
++#include <stdlib.h>
+ int
+ main ()
+ {