Add a script in contrib to download a cmake binary (#19632)

* Add a script in contrib to download a cmake binary

will help on Ubuntu 14.04 and other distros when we upgrade to a
version of LLVM that requires cmake 3.4.3 or newer

* Run in deps/scratch, fix shasum invocation on darwin

contrib/download_cmake.sh

@@ -0,0 +1,40 @@
+#!/bin/sh
+# This file is a part of Julia. License is MIT: http://julialang.org/license
+
+# Script to download newest version of cmake on linux (or mac)
+# saves you the trouble of compiling it if you don't have root
+set -e # stop on failure
+mkdir -p "$(dirname "$0")"/../deps/scratch
+cd "$(dirname "$0")"/../deps/scratch
+
+CMAKE_VERSION_MAJOR=3
+CMAKE_VERSION_MINOR=7
+CMAKE_VERSION_PATCH=1
+CMAKE_VERSION_MAJMIN=$CMAKE_VERSION_MAJOR.$CMAKE_VERSION_MINOR
+CMAKE_VERSION=$CMAKE_VERSION_MAJMIN.$CMAKE_VERSION_PATCH
+
+# listed at https://cmake.org/files/v$CMAKE_VERSION_MAJMIN/cmake-$CMAKE_VERSION-SHA-256.txt
+# for the files cmake-$CMAKE_VERSION-Darwin-x86_64.tar.gz
+# and cmake-$CMAKE_VERSION-Linux-x86_64.tar.gz
+CMAKE_SHA256_DARWIN=1851d1448964893fdc5a8c05863326119f397a3790e0c84c40b83499c7960267
+CMAKE_SHA256_LINUX=7b4b7a1d9f314f45722899c0521c261e4bfab4a6b532609e37fef391da6bade2
+
+PLATFORM="$(uname)-$(uname -m)"
+FULLNAME=cmake-$CMAKE_VERSION-$PLATFORM
+case $PLATFORM in
+  Darwin-x86_64)
+    ../tools/jldownload https://cmake.org/files/v$CMAKE_VERSION_MAJMIN/$FULLNAME.tar.gz
+    echo "$CMAKE_SHA256_DARWIN $FULLNAME.tar.gz" | shasum -a 256 -c -
+    CMAKE_EXTRACTED_PATH=$FULLNAME/CMake.app/Contents/bin/cmake;;
+  Linux-x86_64)
+    ../tools/jldownload https://cmake.org/files/v$CMAKE_VERSION_MAJMIN/$FULLNAME.tar.gz
+    echo "$CMAKE_SHA256_LINUX $FULLNAME.tar.gz" | sha256sum -c -
+    CMAKE_EXTRACTED_PATH=$FULLNAME/bin/cmake;;
+  *)
+    echo "This script only supports x86_64 Mac and Linux. For other platforms," >&2
+    echo "get cmake from your package manager or compile it from source." >&2
+    exit 1;;
+esac
+
+tar -xzf $FULLNAME.tar.gz
+echo "CMAKE = $PWD/$CMAKE_EXTRACTED_PATH" >> ../../Make.user

deps/llvm.mk

@@ -509,7 +509,8 @@ $(LLVM_BUILDDIR_withtype)/build-configured: $(LLVM_SRC_DIR)/source-extracted | $
 	mkdir -p $(dir $@)
 	cd $(dir $@) && \
 		export PATH=$(llvm_python_workaround):$$PATH && \
-		$(CMAKE) $(LLVM_SRC_DIR) $(CMAKE_GENERATOR_COMMAND) $(CMAKE_COMMON) $(LLVM_CMAKE)
+		$(CMAKE) $(LLVM_SRC_DIR) $(CMAKE_GENERATOR_COMMAND) $(CMAKE_COMMON) $(LLVM_CMAKE) \
+		|| { echo '*** To install a newer version of cmake, run contrib/download_cmake.sh ***' && false; }
 	echo 1 > $@
 
 $(LLVM_BUILDDIR_withtype)/build-compiled: $(LLVM_BUILDDIR_withtype)/build-configured | $(llvm_python_workaround)