Fix character encoding when piping stdout on Windows

[michelou]

Character encoding is wrong when piping stdout on Windows, e.g. test case test\run\productElementName.scala contains UTF-8 characters and fails with the following output:

[info] Test dotty.tools.dotc.CompilationTests.runAll started
Output from "tests\run\productElementName.scala" did not match check file.6s)
Diff (expected on the left, actual right):
User(name=Susan, age=42)                             |  User(name=Susan, age=42)
????(??=Susan, ??=42)                                |  ????(??=Susan, ??=42)
U$er(na$me=Susan, a$ge=42)                           |  U$er(na$me=Susan, a$ge=42)
type(for=Susan, if=42)                               |  type(for=Susan, if=42)
contains spaces(first param=Susan, second param=42)  |  contains spaces(first param=Susan, second param=42)
Symbols(::=Susan, ||=42)                             |  Symbols(::=Susan, ||=42)
MultipleParamLists(a=Susan, b=42)                    |  MultipleParamLists(a=Susan, b=42)
AuxiliaryConstructor(a=Susan, b=42)                  |  AuxiliaryConstructor(a=Susan, b=42)
OverloadedApply(a=Susan, b=123)                      |  OverloadedApply(a=Susan, b=123)
PrivateMembers(a=10, b=20, c=30, d=40, e=50, f=60)   |  PrivateMembers(a=10, b=20, c=30, d=40, e=50, f=60)

NoParams()                                           |  NoParams()
EOF                                                  |  EOF

[=======================================] completed (1123/1123, 1 failed, 101s)
[error] Test dotty.tools.dotc.CompilationTests.runAll failed: java.lang.AssertionError: Run test failed, but should not, reasons:
[error]
[error]   - encountered 1 test failures(s), took 113.944 sec
[error]     at dotty.tools.vulpix.ParallelTesting$CompilationTest.checkRuns(ParallelTesting.scala:1008)
[error]     at dotty.tools.dotc.CompilationTests.runAll(CompilationTests.scala:176)
[error]     ...

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[michelou]

See also Problems with UTF-8 support for Windows.