Allow a newline or a tab at the begining of a linker script

Previously, the first four byte must have been "printable" bytes,
which exclude newlines or tabs.

common/filetype.h

@@ -25,9 +25,13 @@ enum class FileType {
 
 template <typename MappedFile>
 bool is_text_file(MappedFile *mf) {
+  auto istext = [](char c) {
+    return isprint(c) || c == '\n' || c == '\t';
+  };
+
   u8 *data = mf->data;
-  return mf->size >= 4 && isprint(data[0]) && isprint(data[1]) &&
-         isprint(data[2]) && isprint(data[3]);
+  return mf->size >= 4 && istext(data[0]) && istext(data[1]) &&
+         istext(data[2]) && istext(data[3]);
 }
 
 template <typename E, typename Context, typename MappedFile>

test/elf/linker-script6.sh

@@ -0,0 +1,15 @@
+#!/bin/bash
+. $(dirname $0)/common.inc
+
+mkdir -p $t/foo
+
+cat <<EOF | $CC -o $t/foo/a.o -c -xc -
+int main() {}
+EOF
+
+cat <<EOF > $t/foo/b.script
+
+INPUT(a.o)
+EOF
+
+$CC -B. -o $t/exe $t/foo/b.script