Fix build tags that use ! multiple times on one line. Those don't actually do anything since build tags use OR within the line. So something like //+build !windows, !linux would actually build on both linux and windows. What was intended in all these cases was probably AND, which you get by splitting them into separate lines.

core/debug/trace/trace_nil.odin

@@ -1,4 +1,6 @@
-//+build !windows !linux !darwin
+//+build !windows
+//+build !linux
+//+build !darwin
 package debug_trace
 
 import "base:runtime"

core/flags/errors_nonbsd.odin

@@ -1,4 +1,5 @@
-//+build !netbsd !openbsd
+//+build !netbsd
+//+build !openbsd
 package flags
 
 import "base:runtime"

core/flags/internal_rtti_nonbsd.odin

@@ -1,5 +1,6 @@
 //+private
-//+build !netbsd !openbsd
+//+build !netbsd
+//+build !openbsd
 package flags
 
 import "core:net"

core/testing/signal_handler_other.odin

@@ -1,5 +1,11 @@
 //+private
-//+build !windows !linux !darwin !freebsd !openbsd !netbsd !haiku
+//+build !windows
+//+build !linux
+//+build !darwin
+//+build !freebsd
+//+build !openbsd
+//+build !netbsd
+//+build !haiku
 package testing
 
 /*

tests/core/net/test_core_net.odin

@@ -10,7 +10,8 @@
 
 	A test suite for `core:net`
 */
-//+build !netbsd !openbsd
+//+build !netbsd
+//+build !openbsd
 package test_core_net
 
 import "core:testing"