fix speculative usage of <sys/shm.h> in AFL runtime (#1278)

Changes

@@ -264,6 +264,9 @@ Working version
 - GPR#1275: correct configure test for Spacetime availability
   (Mark Shinwell)
 
+- GPR#1278: discover presence of <sys/shm.h> during configure for afl runtime
+  (Hannes Mehnert)
+
 ### Internal/compiler-libs changes:
 
 - MPR#6826, GPR#828, GPR#834: improve compilation time for open

byterun/afl.c

@@ -13,9 +13,9 @@
 /**************************************************************************/
 
 /* Runtime support for afl-fuzz */
+#include "caml/config.h"
 
-/* Android's libc does not implement System V shared memory. */
-#if defined(_WIN32) || defined(__ANDROID__)
+#if !defined(HAS_SYS_SHM_H)
 
 #include "caml/mlvalues.h"
 
@@ -159,4 +159,4 @@ CAMLprim value caml_reset_afl_instrumentation(value full)
   return Val_unit;
 }
 
-#endif /* _WIN32 */
+#endif /* HAS_SYS_SHM_H */

configure

@@ -1541,6 +1541,10 @@ if sh ./hasgot getauxval; then
   echo "#define HAS_GETAUXVAL" >> s.h
 fi
 
+if sh ./hasgot -i sys/shm.h; then
+  inf "sys/shm.h found."
+  echo "#define HAS_SYS_SHM_H" >> s.h
+fi
 
 # Determine if the debugger is supported