[source] firmware-utils: fix compilation on MacOS X

[LEDE Commits]

jow pushed a commit to source.git, branch master:
https://git.lede-project.org/00d1e6c75e0a3317331e2e8a9d3e426f0cdc8584

commit 00d1e6c75e0a3317331e2e8a9d3e426f0cdc8584
Author: Alexandru Ardelean <ardeleanalex at gmail.com>
AuthorDate: Fri Oct 28 09:52:12 2016 +0300

    firmware-utils: fix compilation on MacOS X
    
    Looking into /usr/include/stdlib.h, there's a `devname()` function defined
    under some #ifdef's which conflicts with the `static char *devname` definition
    in `src/mkwrggimg.c`.
    
    Defining `_ANSI_SOURCE` in the `src/mkwrggimg.c` file, omits that part of the
    header.
    
    Another more intrusive approach is to rename `devname` to something like
    `g_devname` in `src/mkwrggimg.c`. But I think the `_ANSI_SOURCE` define should
    be enough.
    
    Compilation error is:
    
        src/mkwrggimg.c:64:14: error: redefinition of 'devname' as different kind of symbol
        static char *devname;
                     ^
        /usr/include/stdlib.h:286:7: note: previous definition is here
        char    *devname(dev_t, mode_t);
                 ^
        src/mkwrggimg.c:147:12: error: non-object type 'char *(dev_t, mode_t)' (aka 'char *(int, unsigned short)') is not assignable
                                devname = optarg;
                                ~~~~~~~ ^
        src/mkwrggimg.c:192:6: warning: comparison of function 'devname' equal to a null pointer is always false [-Wtautological-pointer-compare]
                if (devname == NULL) {
                    ^~~~~~~    ~~~~
        src/mkwrggimg.c:192:6: note: prefix with the address-of operator to silence this warning
                if (devname == NULL) {
                    ^
                    &
        src/mkwrggimg.c:251:27: warning: incompatible pointer types passing 'char *(dev_t, mode_t)' (aka 'char *(int, unsigned short)') to parameter of type 'const char *' [-Wincompatible-pointer-types]
                strncpy(header->devname, devname, sizeof(header->devname));
                                         ^~~~~~~
        /usr/include/secure/_string.h:119:34: note: expanded from macro 'strncpy'
          __builtin___strncpy_chk (dest, src, len, __darwin_obsz (dest))
    
    Signed-off-by: Alexandru Ardelean <ardeleanalex at gmail.com>
    [Jo-Philipp Wich: slightly reformat commit message]
    Signed-off-by: Jo-Philipp Wich <jo at mein.io>
---
 tools/firmware-utils/src/mkwrggimg.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/tools/firmware-utils/src/mkwrggimg.c b/tools/firmware-utils/src/mkwrggimg.c
index a224b25..9995b9a 100644
--- a/tools/firmware-utils/src/mkwrggimg.c
+++ b/tools/firmware-utils/src/mkwrggimg.c
@@ -8,6 +8,7 @@
  *
  */
 
+#define _ANSI_SOURCE
 #include <stdio.h>
 #include <stdlib.h>
 #include <stdint.h>