builtin: bootstrap for backtrace functions cleanup

vlib/builtin/cfns.c.v

@@ -27,12 +27,9 @@ fn C.popen(c byteptr, t byteptr) voidptr
 
 // <execinfo.h>
 // backtrace functions are not #included, that's why they have to be defined without C.
-fn backtrace(a voidptr, b int) int
-
-fn backtrace_symbols(voidptr, int)  &byteptr
-
-
-fn backtrace_symbols_fd(voidptr, int, int)
+fn backtrace(a &voidptr, b int) int
+fn backtrace_symbols(a &voidptr, size int)  &charptr
+fn backtrace_symbols_fd(a &voidptr, size int, fd int) void
 // <libproc.h>
 fn proc_pidpath(int, voidptr, int) int
 

vlib/v/gen/cheaders.v

@@ -69,7 +69,20 @@ typedef int (*qsort_callback_func)(const void*, const void*);
 #ifdef __cplusplus
 #include <utility>
 #define _MOV std::move
-#include <execinfo.h>
+#endif
+
+#if defined(__ANDROID__)
+int backtrace (void **__array, int __size) { return 0; }
+char **backtrace_symbols (void *const *__array, int __size){ return 0; }
+void backtrace_symbols_fd (void *const *__array, int __size, int __fd){}
+#else
+#ifndef _WIN32
+#if defined __has_include
+#if __has_include (<execinfo.h>)
+#	include <execinfo.h>
+#endif
+#endif
+#endif
 #endif
 
 //#include "fns.h"

vlib/v/gen/fn.v

@@ -22,6 +22,12 @@ fn (mut g Gen) gen_fn_decl(it ast.FnDecl) {
 	if g.attr == 'inline' {
 		g.write('inline ')
 	}
+	if it.name in ['backtrace', 'backtrace_symbols', 'backtrace_symbols_fd'] {
+		// these are actually defined as C functions in execinfo.h
+		// TODO: remove this check, *after* they are defined as C. in cfns.c.v
+		// in bootstrap phase 2
+		return
+	}
 	//
 	is_livefn := g.attr == 'live'
 	is_livemain := g.pref.is_livemain && is_livefn