Add zig build system

src/getauxval_backport.c

@@ -0,0 +1,67 @@
+#include <elf.h>
+#include <stddef.h>
+#include <stdio.h>
+
+#ifdef GETAUXVAL_BACKPORT_ELF64
+typedef Elf64_auxv_t __auxv_t;
+#else
+typedef Elf32_auxv_t __auxv_t;
+#endif
+
+#define AUXV_FILE "/proc/self/auxv"
+
+#ifdef GETAUXVAL_BACKPORT_FILE
+
+unsigned long __getauxval_file(unsigned long type) {
+  FILE *f = fopen(AUXV_FILE, "rb");
+  if (f == NULL)
+    return 1;
+
+  unsigned long val = 0;
+  __auxv_t aux;
+
+  while (fread(&aux, sizeof(aux), 1, f) == 1 && aux.a_type != AT_NULL) {
+    if (aux.a_type == type) {
+      val = aux.a_un.a_val;
+      break;
+    }
+  }
+
+  fclose(f);
+
+  return val;
+}
+
+#else
+
+extern char **environ;
+
+char **envp_auxv = NULL;
+
+unsigned long __getauxval_envp(unsigned long type) {
+  if (envp_auxv == NULL) {
+    envp_auxv = environ;
+    while (*envp_auxv++ != NULL)
+      ;
+  }
+
+  __auxv_t *auxv;
+
+  for (auxv = (__auxv_t *)envp_auxv; auxv->a_type != AT_NULL; auxv++) {
+    if (auxv->a_type == type) {
+      return auxv->a_un.a_val;
+    }
+  }
+
+  return 0;
+}
+
+#endif
+
+unsigned long getauxval(unsigned long type) {
+#ifdef GETAUXVAL_BACKPORT_FILE
+  return __getauxval_file(type);
+#else
+  return __getauxval_envp(type);
+#endif
+}