libc: implement common abs for various integer sizes

lib/c.zig

@@ -14,6 +14,9 @@ else
     std.debug.no_panic;
 
 comptime {
+    _ = @import("c/inttypes.zig");
+    _ = @import("c/stdlib.zig");
+
     if (builtin.target.isMuslLibC() or builtin.target.isWasiLibC()) {
         // Files specific to musl and wasi-libc.
         _ = @import("c/string.zig");

lib/c/inttypes.zig

@@ -0,0 +1,20 @@
+const std = @import("std");
+const common = @import("common.zig");
+const builtin = @import("builtin");
+const intmax_t = std.c.intmax_t;
+
+comptime {
+    if (builtin.target.isMuslLibC() or builtin.target.isWasiLibC()) {
+        // Functions specific to musl and wasi-libc.
+        @export(&imaxabs, .{ .name = "imaxabs", .linkage = common.linkage, .visibility = common.visibility });
+    }
+}
+
+fn imaxabs(a: intmax_t) callconv(.c) intmax_t {
+    return @intCast(@abs(a));
+}
+
+test imaxabs {
+    const val: intmax_t = -10;
+    try std.testing.expectEqual(10, imaxabs(val));
+}

lib/c/stdlib.zig

@@ -0,0 +1,39 @@
+const std = @import("std");
+const common = @import("common.zig");
+const builtin = @import("builtin");
+
+comptime {
+    if (builtin.target.isMuslLibC() or builtin.target.isWasiLibC()) {
+        // Functions specific to musl and wasi-libc.
+        @export(&abs, .{ .name = "abs", .linkage = common.linkage, .visibility = common.visibility });
+        @export(&labs, .{ .name = "labs", .linkage = common.linkage, .visibility = common.visibility });
+        @export(&llabs, .{ .name = "llabs", .linkage = common.linkage, .visibility = common.visibility });
+    }
+}
+
+fn abs(a: c_int) callconv(.c) c_int {
+    return @intCast(@abs(a));
+}
+
+fn labs(a: c_long) callconv(.c) c_long {
+    return @intCast(@abs(a));
+}
+
+fn llabs(a: c_longlong) callconv(.c) c_longlong {
+    return @intCast(@abs(a));
+}
+
+test abs {
+    const val: c_int = -10;
+    try std.testing.expectEqual(10, abs(val));
+}
+
+test labs {
+    const val: c_long = -10;
+    try std.testing.expectEqual(10, labs(val));
+}
+
+test llabs {
+    const val: c_longlong = -10;
+    try std.testing.expectEqual(10, llabs(val));
+}