vendor/libc: a bunch of additions

All these additions are to allow Dear ImGui to be compiled natively.

vendor/libc/stdlib.odin

@@ -1,8 +1,10 @@
 package odin_libc
 
+import "base:intrinsics"
 import "base:runtime"
 
 import "core:c"
+import "core:os"
 import "core:slice"
 import "core:sort"
 import "core:strconv"
@@ -108,12 +110,81 @@ atof :: proc "c" (str: cstring) -> f64 {
 @(require, linkage="strong", link_name="strtol")
 strtol :: proc "c" (str: cstring, str_end: ^cstring, base: i32) -> c.long {
 	context = g_ctx
-
 	sstr := string(str)
 	sstr  = strings.trim_left_space(sstr)
 
 	n: int
 	i, _ := strconv.parse_i64_of_base(sstr, int(base), &n)
 	str_end ^= cstring(raw_data(sstr)[n:])
+	if str_end != nil {
+		str_end ^= cstring(raw_data(sstr)[n:])
+	}
 	return c.long(clamp(i, i64(min(c.long)), i64(max(c.long))))
 }
+
+@(require, linkage="strong", link_name="strtod")
+strtod :: proc "c" (str: cstring, str_end: ^cstring) -> c.double {
+	context = g_ctx
+
+	sstr := string(str)
+	sstr  = strings.trim_left_space(sstr)
+
+	n: int
+	val, _ := strconv.parse_f64(sstr, &n)
+	if str_end != nil {
+		str_end ^= cstring(raw_data(sstr)[n:])
+	}
+
+	return c.double(val)
+}
+
+@(require, linkage="strong", link_name="abort")
+abort :: proc "c" () -> ! {
+	intrinsics.trap()
+}
+
+ATEXIT_MAX :: 32
+
+@(private)
+atexit_functions: [ATEXIT_MAX]proc "c" ()
+@(private)
+atexit_functions_count: int
+
+@(require, linkage="strong", link_name="atexit")
+atexit :: proc "c" (function: proc "c" ()) -> i32 {
+	entry := intrinsics.atomic_add(&atexit_functions_count, 1)
+	if entry >= ATEXIT_MAX {
+		return -1
+	}
+
+	atexit_functions[entry] = function
+	return 0
+}
+
+
+@(require, linkage="strong", link_name="exit")
+exit :: proc "c" (exit_code: c.int) -> ! {
+	finish_atexit()
+	os.exit(int(exit_code))
+}
+
+@(private, fini)
+finish_atexit :: proc "c" () {
+	n := intrinsics.atomic_exchange(&atexit_functions_count, 0)
+	for function in atexit_functions[:n] {
+		function()
+	}
+}
+
+ldiv_t :: struct {
+	quot: c.long,
+	rem:  c.long,
+}
+
+@(require, linkage="strong", link_name="ldiv")
+ldiv :: proc "c" (number: c.long, denom: c.long) -> ldiv_t {
+	return {
+		quot = number  / denom,
+		rem  = number %% denom,
+	}
+}