libsysprof-capture: Use malloc() rather than g_new0() and friends

Another step away from GLib. This changes the OOM behaviour of the
library — previously it would immediately `abort()` on OOM. However, it
seems likely that given the small number of allocations
libsysprof-capture does, it should be able to recover from an OOM
situation more gracefully than larger libraries can — so the new
implementation tries to do that.

Signed-off-by: Philip Withnall <withnall@endlessm.com>

Helps: #40

src/libsysprof-capture/sysprof-capture-util-private.h

@@ -62,8 +62,20 @@
 # include <sys/sendfile.h>
 #endif
 
+#include <stdlib.h>
+#include <string.h>
 #include <unistd.h>
 
+static inline void *
+sysprof_malloc0 (size_t size)
+{
+  void *ptr = malloc (size);
+  if (ptr == NULL)
+    return NULL;
+  memset (ptr, 0, size);
+  return ptr;
+}
+
 #ifdef __linux__
 # define _sysprof_getpagesize()     getpagesize()
 # define _sysprof_pread(a,b,c,d)    pread(a,b,c,d)