[gpsd-dev] SHM broken

[Hal Murray]

I noticed a SHM warning in a log file.

It's right after the can't find libkern/OSAtomic.h message so
it looks like SHM depends on a strange file I 've never heard of before.

>From the log file:
  Checking if compiler is C11 ...(cached) no
  Checking for C header file libkern/OSAtomic.h... (cached) no
  No memory barriers - SHM export and time hinting may not be reliable.

Looking at the code in SConstruct
    # check for C11 or better, and __STDC__NO_ATOMICS__ is no defined
    # before looking for stdatomic.h

gpsd_config.h says:
/* #undef HAVE_STDATOMIC_H */
/* #undef HAVE_OSATOMIC_H */

I've got an up to date Fedora box.
  gcc (GCC) 4.9.2 20150212 (Red Hat 4.9.2-6)
  /usr/lib/gcc/i686-redhat-linux/4.9.2/include/stdatomic.h

google found stuff with "-std=c11" on the command line for gcc.  The man page 
for gcc says the default is gnu89 with lots of fine print.  grep -w doesn't 
find any "std" in SConstruct.



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