[Branch-Rename] Fix some links

According to the [[ https://foundation.llvm.org/docs/branch-rename/ | status of branch rename ]], the master branch of the LLVM repository is removed on 28 Jan 2021.

Reviewed By: mehdi_amini

Differential Revision: https://reviews.llvm.org/D95766

GitOrigin-RevId: 94fac81fccfef9917e94bed398781744fb82e159
diff --git a/docs/resources/build.rst b/docs/resources/build.rst
index 0ce76dd..7c2a431 100644
--- a/docs/resources/build.rst
+++ b/docs/resources/build.rst
@@ -12,7 +12,7 @@
 general instructions on how to check out the LLVM monorepo, which contains the
 LLDB sources.
 
-Git browser: https://github.com/llvm/llvm-project/tree/master/lldb
+Git browser: https://github.com/llvm/llvm-project/tree/main/lldb
 
 Preliminaries
 -------------
@@ -326,7 +326,7 @@
 A cache is passed to CMake with the ``-C`` flag, following the absolute path to
 the file on disk. Subsequent ``-D`` options are still allowed. Please find the
 currently available caches in the `lldb/cmake/caches/
-<https://github.com/llvm/llvm-project/tree/master/lldb/cmake/caches>`_
+<https://github.com/llvm/llvm-project/tree/main/lldb/cmake/caches>`_
 directory.
 
 Common configurations on macOS
diff --git a/docs/resources/test.rst b/docs/resources/test.rst
index 61db746..e70e60e 100644
--- a/docs/resources/test.rst
+++ b/docs/resources/test.rst
@@ -99,10 +99,10 @@
 several extensions and custom test primitives on top of what's offered by
 `unittest2 <https://docs.python.org/2/library/unittest.html>`_. Those can be
 found  in
-`lldbtest.py <https://github.com/llvm/llvm-project/blob/master/lldb/packages/Python/lldbsuite/test/lldbtest.py>`_.
+`lldbtest.py <https://github.com/llvm/llvm-project/blob/main/lldb/packages/Python/lldbsuite/test/lldbtest.py>`_.
 
 Below is the directory layout of the `example API test
-<https://github.com/llvm/llvm-project/tree/master/lldb/test/API/sample_test>`_.
+<https://github.com/llvm/llvm-project/tree/main/lldb/test/API/sample_test>`_.
 The test directory will always contain a python file, starting with ``Test``.
 Most of the tests are structured as a binary being debugged, so there will be
 one or more source files and a ``Makefile``.
@@ -127,7 +127,7 @@
 operations, such as creating targets, setting breakpoints etc. When code is
 shared across tests, we extract it into a utility in ``lldbutil``. It's always
 worth taking a look at  `lldbutil
-<https://github.com/llvm/llvm-project/blob/master/lldb/packages/Python/lldbsuite/test/lldbutil.py>`_
+<https://github.com/llvm/llvm-project/blob/main/lldb/packages/Python/lldbsuite/test/lldbutil.py>`_
 to see if there's a utility to simplify some of the testing boiler plate.
 Because we can't always audit every existing test, this is doubly true when
 looking at an existing test for inspiration.
@@ -168,7 +168,7 @@
   include Makefile.rules
 
 Finding the right variables to set can be tricky. You can always take a look at
-`Makefile.rules <https://github.com/llvm/llvm-project/blob/master/lldb/packages/Python/lldbsuite/test/make/Makefile.rules>`_
+`Makefile.rules <https://github.com/llvm/llvm-project/blob/main/lldb/packages/Python/lldbsuite/test/make/Makefile.rules>`_
 but often it's easier to find an existing ``Makefile`` that does something
 similar to what you want to do.
 
diff --git a/docs/use/python-reference.rst b/docs/use/python-reference.rst
index 92d259b..e5542bb 100644
--- a/docs/use/python-reference.rst
+++ b/docs/use/python-reference.rst
@@ -420,11 +420,11 @@
 There is a longer discussion of scripted thread plans and the state machine,
 and several interesting examples of their use in:
 
-https://github.com/llvm/llvm-project/blob/master/lldb/examples/python/scripted_step.py
+https://github.com/llvm/llvm-project/blob/main/lldb/examples/python/scripted_step.py
 
 And for a MUCH fuller discussion of the whole state machine, see:
 
-https://github.com/llvm/llvm-project/blob/master/lldb/include/lldb/Target/ThreadPlan.h
+https://github.com/llvm/llvm-project/blob/main/lldb/include/lldb/Target/ThreadPlan.h
 
 If you are reading those comments it is useful to know that scripted thread
 plans are set to be "MasterPlans", and not "OkayToDiscard".
@@ -625,7 +625,7 @@
 A more interesting template has been created in the source repository that can
 help you to create lldb command quickly:
 
-https://github.com/llvm/llvm-project/blob/master/lldb/examples/python/cmdtemplate.py
+https://github.com/llvm/llvm-project/blob/main/lldb/examples/python/cmdtemplate.py
 
 A commonly required facility is being able to create a command that does some
 token substitution, and then runs a different debugger command (usually, it