Make gcc_solink_wrapper.py work with Python 3.

This is sort of a reland of https://crrev.com/c/2260872, but rather than
calling bytes.decode() on every line we pass |universal_newlines=True| to
subprocess.Popen() so that |lines| is still a string and not a bytes object
in Python 3.

This approach does not cause the significant slowdown during linking that
led to the previous CL being reverted.

Bug: 941669
Change-Id: I92bc14d4dea01085f9f81153f610663960cc2fcf
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2263712
Commit-Queue: Nico Weber <thakis@chromium.org>
Auto-Submit: Raphael Kubo da Costa <raphael.kubo.da.costa@intel.com>
Reviewed-by: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#781825}

build/toolchain/gcc_solink_wrapper.py

@@ -23,7 +23,10 @@ def CollectSONAME(args):
   """Replaces: readelf -d $sofile | grep SONAME"""
   toc = ''
   readelf = subprocess.Popen(wrapper_utils.CommandToRun(
-      [args.readelf, '-d', args.sofile]), stdout=subprocess.PIPE, bufsize=-1)
+      [args.readelf, '-d', args.sofile]),
+                             stdout=subprocess.PIPE,
+                             bufsize=-1,
+                             universal_newlines=True)
   for line in readelf.stdout:
     if 'SONAME' in line:
       toc += line
@@ -33,11 +36,11 @@ def CollectSONAME(args):
 def CollectDynSym(args):
   """Replaces: nm --format=posix -g -D -p $sofile | cut -f1-2 -d' '"""
   toc = ''
-  nm = subprocess.Popen(
-      wrapper_utils.CommandToRun(
-          [args.nm, '--format=posix', '-g', '-D', '-p', args.sofile]),
-      stdout=subprocess.PIPE,
-      bufsize=-1)
+  nm = subprocess.Popen(wrapper_utils.CommandToRun(
+      [args.nm, '--format=posix', '-g', '-D', '-p', args.sofile]),
+                        stdout=subprocess.PIPE,
+                        bufsize=-1,
+                        universal_newlines=True)
   for line in nm.stdout:
     toc += ' '.join(line.split(' ', 2)[:2]) + '\n'
   return nm.wait(), toc