fix build after PR ziglang/zig#20388

Author: StringNick

build.zig

@@ -29,12 +29,12 @@ fn buildSecp256k1(libsecp_c: *std.Build.Dependency, b: *std.Build, target: std.B
             "./src/precomputed_ecmult_gen.c",
         },
     });
-    lib.defineCMacro("USE_FIELD_10X26", "1");
-    lib.defineCMacro("USE_SCALAR_8X32", "1");
-    lib.defineCMacro("USE_ENDOMORPHISM", "1");
-    lib.defineCMacro("USE_NUM_NONE", "1");
-    lib.defineCMacro("USE_FIELD_INV_BUILTIN", "1");
-    lib.defineCMacro("USE_SCALAR_INV_BUILTIN", "1");
+    lib.root_module.addCMacro("USE_FIELD_10X26", "1");
+    lib.root_module.addCMacro("USE_SCALAR_8X32", "1");
+    lib.root_module.addCMacro("USE_ENDOMORPHISM", "1");
+    lib.root_module.addCMacro("USE_NUM_NONE", "1");
+    lib.root_module.addCMacro("USE_FIELD_INV_BUILTIN", "1");
+    lib.root_module.addCMacro("USE_SCALAR_INV_BUILTIN", "1");
 
     lib.installHeadersDirectory(libsecp_c.path("src"), "", .{ .include_extensions = &.{".h"} });
     lib.installHeadersDirectory(libsecp_c.path("include/"), "", .{ .include_extensions = &.{".h"} });