Use C to force the POSIX (not GNU) overload of strerror_r to be selected

This allows building TSC for Android without needing to pass custom flags via -Xcc.

Author: jakepetroules

Sources/TSCBasic/misc.swift

@@ -8,6 +8,7 @@
  See http://swift.org/CONTRIBUTORS.txt for Swift project authors
 */
 
+@_implementationOnly import TSCclibc
 import TSCLibc
 import Foundation
 #if os(Windows)
@@ -327,7 +328,7 @@ extension SystemError: CustomStringConvertible {
             var cap = 64
             while cap <= 16 * 1024 {
                 var buf = [Int8](repeating: 0, count: cap)
-                let err = TSCLibc.strerror_r(errno, &buf, buf.count)
+                let err = TSCclibc.tsc_strerror_r(errno, &buf, buf.count)
                 if err == EINVAL {
                     return "Unknown error \(errno)"
                 }

Sources/TSCclibc/CMakeLists.txt

@@ -7,7 +7,7 @@
 # See http://swift.org/CONTRIBUTORS.txt for Swift project authors
 
 add_library(TSCclibc STATIC
-  libc.c process.c)
+  libc.c process.c strerror.c)
 target_include_directories(TSCclibc PUBLIC
   include)
 target_compile_definitions(TSCclibc PRIVATE

Sources/TSCclibc/include/module.modulemap

@@ -2,5 +2,6 @@ module TSCclibc {
     header "TSCclibc.h"
     header "indexstore_functions.h"
     header "process.h"
+    header "strerror.h"
     export *
 }

Sources/TSCclibc/include/strerror.h

@@ -0,0 +1,3 @@
+#include <stddef.h>
+
+extern int tsc_strerror_r(int errnum, char *buf, size_t buflen);

Sources/TSCclibc/strerror.c

@@ -0,0 +1,7 @@
+#undef _GNU_SOURCE
+#include "strerror.h"
+#include <string.h>
+
+int tsc_strerror_r(int errnum, char *buf, size_t buflen) {
+    return strerror_r(errnum, buf, buflen);
+}