statically link xz (#74)

See #71, #72, #73. Our `xz` is picking up travis's `xz` installation and using its (incompatible) `liblzma` shared library. On the suggestion of @stuhood in pantsbuild/pants#5936, we statically link `xz` here to avoid ever having this problem ever again. Proof:
*linux*:
```
> ldd ./xz-5.2.4-linux/xz-install/bin/xz
        linux-vdso.so.1 (0x00007ffc865cd000)
        libpthread.so.0 => /usr/lib/libpthread.so.0 (0x00007f1fa385f000)
        libc.so.6 => /usr/lib/libc.so.6 (0x00007f1fa34a3000)
        /lib64/ld-linux-x86-64.so.2 => /usr/lib64/ld-linux-x86-64.so.2 (0x00007f1fa3cb4000)
```
*osx*:
```
> otool -L ./xz-5.2.4-linux/xz-install/bin/xz
./xz-5.2.4-linux/xz-install/bin/xz:
	/usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 1252.50.4)
```

build-support/bin/xz/linux/x86_64/5.2.4-3/build-xz.sh

@@ -0,0 +1,64 @@
+#!/bin/bash
+
+source "$(git rev-parse --show-toplevel)/utils.v1.bash"
+
+set_strict_mode
+
+function package_xz {
+  local -r installed_dir_abs="$1"
+
+  with_pushd "$installed_dir_abs" \
+             create_gz_package 'xz' bin
+}
+
+function fetch_extract_xz_source_release {
+  local -r archive_dirname="xz-${XZ_VERSION}"
+  local -r archive_filename="${archive_dirname}.tar.gz"
+  local -r release_url="https://tukaani.org/xz/${archive_filename}"
+
+  local -r downloaded_archive="$(curl_file_with_fail "$release_url" "$archive_filename")"
+  extract_for "$downloaded_archive" "$archive_dirname"
+}
+
+function build_xz {
+  local -r install_dir_abs="$1"
+
+  # We statically link the `xz` executable to avoid conflicts with any liblzma.so on the host
+  # machine (see pantsbuild/pants#5639).
+  ./configure \
+    --enable-static --disable-shared \
+    --prefix="$install_dir_abs"
+
+  make "-j${MAKE_JOBS}"
+
+  make install
+}
+
+function fetch_build_xz {
+  local -r install_dir_abs="$(mkdirp_absolute_path 'xz-install')"
+
+  local -r xz_src_extracted_abs="$(fetch_extract_xz_source_release)"
+
+  with_pushd >&2 "$xz_src_extracted_abs" \
+                 build_xz "$install_dir_abs"
+
+  package_xz "$install_dir_abs"
+}
+
+readonly TARGET_PLATFORM="$1" XZ_VERSION="$2"
+
+readonly MAKE_JOBS="${MAKE_JOBS:-2}"
+
+case "$TARGET_PLATFORM" in
+  osx)
+    with_pushd "$(mkdirp_absolute_path "xz-${XZ_VERSION}-osx")" \
+               fetch_build_xz
+    ;;
+  linux)
+    with_pushd "$(mkdirp_absolute_path "xz-${XZ_VERSION}-linux")" \
+               fetch_build_xz
+    ;;
+  *)
+    die "xz does not support building for '${TARGET_PLATFORM}'"
+    ;;
+esac

build-support/bin/xz/linux/x86_64/5.2.4-3/build.sh

@@ -0,0 +1,5 @@
+#!/bin/bash
+
+readonly result="$(./build-xz.sh linux 5.2.4)"
+
+cp "$result" ./xz.tar.gz

build-support/bin/xz/mac/10.13/5.2.4-3/build-xz.sh

@@ -0,0 +1,64 @@
+#!/bin/bash
+
+source "$(git rev-parse --show-toplevel)/utils.v1.bash"
+
+set_strict_mode
+
+function package_xz {
+  local -r installed_dir_abs="$1"
+
+  with_pushd "$installed_dir_abs" \
+             create_gz_package 'xz' bin
+}
+
+function fetch_extract_xz_source_release {
+  local -r archive_dirname="xz-${XZ_VERSION}"
+  local -r archive_filename="${archive_dirname}.tar.gz"
+  local -r release_url="https://tukaani.org/xz/${archive_filename}"
+
+  local -r downloaded_archive="$(curl_file_with_fail "$release_url" "$archive_filename")"
+  extract_for "$downloaded_archive" "$archive_dirname"
+}
+
+function build_xz {
+  local -r install_dir_abs="$1"
+
+  # We statically link the `xz` executable to avoid conflicts with any liblzma.so on the host
+  # machine (see pantsbuild/pants#5639).
+  ./configure \
+    --enable-static --disable-shared \
+    --prefix="$install_dir_abs"
+
+  make "-j${MAKE_JOBS}"
+
+  make install
+}
+
+function fetch_build_xz {
+  local -r install_dir_abs="$(mkdirp_absolute_path 'xz-install')"
+
+  local -r xz_src_extracted_abs="$(fetch_extract_xz_source_release)"
+
+  with_pushd >&2 "$xz_src_extracted_abs" \
+                 build_xz "$install_dir_abs"
+
+  package_xz "$install_dir_abs"
+}
+
+readonly TARGET_PLATFORM="$1" XZ_VERSION="$2"
+
+readonly MAKE_JOBS="${MAKE_JOBS:-2}"
+
+case "$TARGET_PLATFORM" in
+  osx)
+    with_pushd "$(mkdirp_absolute_path "xz-${XZ_VERSION}-osx")" \
+               fetch_build_xz
+    ;;
+  linux)
+    with_pushd "$(mkdirp_absolute_path "xz-${XZ_VERSION}-linux")" \
+               fetch_build_xz
+    ;;
+  *)
+    die "xz does not support building for '${TARGET_PLATFORM}'"
+    ;;
+esac

build-support/bin/xz/mac/10.13/5.2.4-3/build.sh

@@ -0,0 +1,5 @@
+#!/bin/bash
+
+readonly result="$(./build-xz.sh linux 5.2.4)"
+
+cp "$result" ./xz.tar.gz