[CMake] Bump CMake minimum version to 3.13.4

This upgrade should be friction-less because we've already been ensuring
that CMake >= 3.13.4 is used.

This is part of the effort discussed on llvm-dev here:

  http://lists.llvm.org/pipermail/llvm-dev/2020-April/140578.html

Differential Revision: https://reviews.llvm.org/D78648

CMakeLists.txt

@@ -1,12 +1,6 @@
 # See docs/CMake.html for instructions about how to build LLVM with CMake.
 
-cmake_minimum_required(VERSION 3.4.3)
-
-if ("${CMAKE_VERSION}" VERSION_LESS "3.13.4")
-  message(FATAL_ERROR
-    "Your CMake version is ${CMAKE_VERSION}. The minimum version of CMake "
-    "required to build LLVM is now 3.13.4.")
-endif()
+cmake_minimum_required(VERSION 3.13.4)
 
 if(POLICY CMP0068)
   cmake_policy(SET CMP0068 NEW)

docs/CMake.rst

@@ -34,7 +34,7 @@ Quick start
 We use here the command-line, non-interactive CMake interface.
 
 #. `Download <http://www.cmake.org/cmake/resources/software.html>`_ and install
-   CMake. Version 3.4.3 is the minimum required.
+   CMake. Version 3.13.4 is the minimum required.
 
 #. Open a shell. Your development tools must be reachable from this shell
    through the PATH environment variable.
@@ -717,7 +717,7 @@ and uses them to build a simple application ``simple-tool``.
 
 .. code-block:: cmake
 
-  cmake_minimum_required(VERSION 3.4.3)
+  cmake_minimum_required(VERSION 3.13.4)
   project(SimpleProject)
 
   find_package(LLVM REQUIRED CONFIG)

docs/CMakePrimer.rst

@@ -54,7 +54,7 @@ program. The example uses only CMake language-defined functions.
 
 .. code-block:: cmake
 
-   cmake_minimum_required(VERSION 3.2)
+   cmake_minimum_required(VERSION 3.15)
    project(HelloWorld)
    add_executable(HelloWorld HelloWorld.cpp)
 
@@ -64,13 +64,13 @@ block to define "APPLE" when targeting Apple platforms:
 
 .. code-block:: cmake
 
-   cmake_minimum_required(VERSION 3.2)
+   cmake_minimum_required(VERSION 3.15)
    project(HelloWorld)
    add_executable(HelloWorld HelloWorld.cpp)
    if(APPLE)
      target_compile_definitions(HelloWorld PUBLIC APPLE)
    endif()
-   
+
 Variables, Types, and Scope
 ===========================
 
@@ -93,7 +93,7 @@ example:
    set(var_name var1)
    set(${var_name} foo) # same as "set(var1 foo)"
    set(${${var_name}}_var bar) # same as "set(foo_var bar)"
-   
+
 Dereferencing an unset variable results in an empty expansion. It is a common
 pattern in CMake to conditionally set variables knowing that it will be used in
 code paths that the variable isn't set. There are examples of this throughout
@@ -107,7 +107,7 @@ An example of variable empty expansion is:
      set(extra_sources Apple.cpp)
    endif()
    add_executable(HelloWorld HelloWorld.cpp ${extra_sources})
-   
+
 In this example the ``extra_sources`` variable is only defined if you're
 targeting an Apple platform. For all other targets the ``extra_sources`` will be
 evaluated as empty before add_executable is given its arguments.
@@ -124,7 +124,7 @@ defining lists:
    # Creates a list with members a, b, c, and d
    set(my_list a b c d)
    set(my_list "a;b;c;d")
-   
+
    # Creates a string "a b c d"
    set(my_string "a b c d")
 
@@ -141,7 +141,7 @@ make a list of variable names that refer to other lists. For example:
    set(a 1 2 3)
    set(b 4 5 6)
    set(c 7 8 9)
-   
+
 With this layout you can iterate through the list of lists printing each value
 with the following code:
 
@@ -152,7 +152,7 @@ with the following code:
        message(${value})
      endforeach()
    endforeach()
-   
+
 You'll notice that the inner foreach loop's list is doubly dereferenced. This is
 because the first dereference turns ``list_name`` into the name of the sub-list
 (a, b, or c in the example), then the second dereference is to get the value of
@@ -385,7 +385,7 @@ result in some unexpected behavior if using unreferenced variables. For example:
        message("${var}")
      endforeach()
    endmacro()
-   
+
    set(my_list a b c d)
    set(my_list_of_numbers 1 2 3 4)
    print_list(my_list_of_numbers)

docs/GettingStarted.rst

@@ -167,7 +167,7 @@ uses the package and provides other details.
 =========================================================== ============ ==========================================
 Package                                                     Version      Notes
 =========================================================== ============ ==========================================
-`CMake <http://cmake.org/>`__                               >=3.4.3      Makefile/workspace generator
+`CMake <http://cmake.org/>`__                               >=3.13.4     Makefile/workspace generator
 `GCC <http://gcc.gnu.org/>`_                                >=5.1.0      C/C++ compiler\ :sup:`1`
 `python <http://www.python.org/>`_                          >=2.7        Automated test suite\ :sup:`2`
 `zlib <http://zlib.net>`_                                   >=1.2.3.4    Compression library\ :sup:`3`

runtimes/CMakeLists.txt

@@ -7,7 +7,7 @@
 # Setting CMake minimum required version should be at the very top of the file
 # if this is the entry point.
 if(CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR)
-  cmake_minimum_required(VERSION 3.4.3)
+  cmake_minimum_required(VERSION 3.13.4)
   project(Runtimes C CXX ASM)
 endif()
 
@@ -56,7 +56,7 @@ if(${CMAKE_SOURCE_DIR} STREQUAL ${CMAKE_CURRENT_SOURCE_DIR})
     set_property(GLOBAL APPEND PROPERTY SUB_COMPONENTS ${name})
   endfunction()
 
-  cmake_minimum_required(VERSION 3.4.3)
+  cmake_minimum_required(VERSION 3.13.4)
   project(Runtimes C CXX ASM)
 
   find_package(LLVM PATHS "${LLVM_BINARY_DIR}" NO_DEFAULT_PATH NO_CMAKE_FIND_ROOT_PATH)

utils/benchmark/CMakeLists.txt

@@ -1,4 +1,4 @@
-cmake_minimum_required (VERSION 2.8.12)
+cmake_minimum_required(VERSION 3.13.4)
 
 # Tell cmake 3.0+ that it's safe to clear the PROJECT_VERSION variable in the
 # call to project() below.