pkg/csource: allow to ignore warnings during build

Running bisection using an older repro failed with:

    <stdin>: In function ‘syz_mount_image.constprop’:
    <stdin>:298:3: error: argument 1 null where non-null expected [-Werror=nonnull]
    In file included from <stdin>:26:0:
    /usr/include/x86_64-linux-gnu/sys/stat.h:320:12: note: in a call to function ‘mkdir’ declared here
     extern int mkdir (const char *__path, __mode_t __mode)

Let's be safe and ignore warnings during repro/bisect.
Everything that runs during tests still has all warnings.

Update #501

1 files changed, 14 insertions, 3 deletions

diff --git a/pkg/csource/build.go b/pkg/csource/build.go
index 35ac28e83..56d5487a8 100644
--- a/pkg/csource/build.go
+++ b/pkg/csource/build.go
@@ -18,15 +18,23 @@ import (
 
 // Build builds a C program from source src and returns name of the resulting binary.
 func Build(target *prog.Target, src []byte) (string, error) {
-	return build(target, src, "")
+	return build(target, src, "", true)
+}
+
+// BuildNoWarn is the same as Build, but ignores all compilation warnings.
+// Should not be used in tests, but may be used e.g. when we are bisecting and potentially
+// using an old repro with newer compiler, or a compiler that we never seen before.
+// In these cases it's more important to build successfully.
+func BuildNoWarn(target *prog.Target, src []byte) (string, error) {
+	return build(target, src, "", false)
 }
 
 // BuildFile builds a C/C++ program from file src and returns name of the resulting binary.
 func BuildFile(target *prog.Target, src string) (string, error) {
-	return build(target, nil, src)
+	return build(target, nil, src, true)
 }
 
-func build(target *prog.Target, src []byte, file string) (string, error) {
+func build(target *prog.Target, src []byte, file string, warn bool) (string, error) {
 	sysTarget := targets.Get(target.OS, target.Arch)
 	compiler := sysTarget.CCompiler
 	if _, err := exec.LookPath(compiler); err != nil {
@@ -55,6 +63,9 @@ func build(target *prog.Target, src []byte, file string) (string, error) {
 		// We do generate uint64's for syscall arguments that overflow longs on 32-bit archs.
 		flags = append(flags, "-Wno-overflow")
 	}
+	if !warn {
+		flags = append(flags, "-fpermissive", "-w")
+	}
 	cmd := osutil.Command(compiler, flags...)
 	if file == "" {
 		cmd.Stdin = bytes.NewReader(src)