Windows: Port icu4c; define cxx std flags for MSVC (spack#45547)

* Adds an MSBuild system + Builder to the icu4c package
* Adds custom install method as MSBuild system does not vendor an
  install target
* The cxxstd variant is not supported on Windows (there are no config
  options you use to tell the build system what cxx standard to
  build against), so the variant definition was updated to occur
  everywhere except Windows

Also, this commit defines the c/cxx..._flag properties of the MSVC
compiler (although they are not used by `icu4c` and not strictly
necessary to bundle with this PR).

lib/spack/spack/compilers/msvc.py

@@ -223,6 +223,30 @@ def get_oneapi_root(pth: str):
             )
         self.msvc_compiler_environment = CmdCall(*env_cmds)
 
+    @property
+    def cxx11_flag(self):
+        return "/std:c++11"
+
+    @property
+    def cxx14_flag(self):
+        return "/std:c++14"
+
+    @property
+    def cxx17_flag(self):
+        return "/std:c++17"
+
+    @property
+    def cxx20_flag(self):
+        return "/std:c++20"
+
+    @property
+    def c11_flag(self):
+        return "/std:c11"
+
+    @property
+    def c17_flag(self):
+        return "/std:c17"
+
     @property
     def msvc_version(self):
         """This is the VCToolset version *NOT* the actual version of the cl compiler

var/spack/repos/builtin/packages/icu4c/package.py

@@ -3,10 +3,12 @@
 #
 # SPDX-License-Identifier: (Apache-2.0 OR MIT)
 
+import pathlib
+
 from spack.package import *
 
 
-class Icu4c(AutotoolsPackage):
+class Icu4c(AutotoolsPackage, MSBuildPackage):
     """ICU is a mature, widely used set of C/C++ and Java libraries providing
     Unicode and Globalization support for software applications. ICU4C is the
     C/C++ interface."""
@@ -31,15 +33,22 @@ class Icu4c(AutotoolsPackage):
     depends_on("c", type="build")  # generated
     depends_on("cxx", type="build")  # generated
 
-    variant(
-        "cxxstd",
-        default="11",
-        values=("11", "14", "17"),
-        multi=False,
-        description="Use the specified C++ standard when building",
-    )
+    build_system("autotools", "msbuild", default="autotools")
+    for plat in ["linux", "darwin", "freebsd"]:
+        with when(f"platform={plat}"):
+            variant(
+                "cxxstd",
+                default="11",
+                values=("11", "14", "17"),
+                multi=False,
+                description="Use the specified C++ standard when building",
+            )
 
     depends_on("python", type="build", when="@64.1:")
+    with when("build_system=autotools"):
+        depends_on("autoconf", type="build")
+        depends_on("automake", type="build")
+        depends_on("libtool", type="build")
 
     conflicts(
         "%intel@:16",
@@ -55,8 +64,6 @@ class Icu4c(AutotoolsPackage):
         when="@58.0:59",
     )
 
-    configure_directory = "source"
-
     def url_for_version(self, version):
         url = "https://github.com/unicode-org/icu/releases/download/release-{0}/icu4c-{1}-src.tgz"
         return url.format(version.dashed, version.underscored)
@@ -68,12 +75,19 @@ def flag_handler(self, name, flags):
             flags.append(getattr(self.compiler, f"cxx{self.spec.variants['cxxstd'].value}_flag"))
         return (None, flags, None)
 
+
+class BuildEnvironment:
     # Need to make sure that locale is UTF-8 in order to process source
     # files in UTF-8.
     @when("@59:")
     def setup_build_environment(self, env):
         env.set("LC_ALL", "en_US.UTF-8")
 
+
+class AutotoolsBuilder(spack.build_systems.autotools.AutotoolsBuilder, BuildEnvironment):
+
+    configure_directory = "source"
+
     def configure_args(self):
         args = []
 
@@ -88,3 +102,33 @@ def configure_args(self):
             args.append("--enable-rpath")
 
         return args
+
+
+class MSBuildBuilder(spack.build_systems.msbuild.MSBuildBuilder, BuildEnvironment):
+    def msbuild_args(self):
+        return [
+            "allinone.sln",
+            self.define("OutputPath", self.spec.prefix),
+            self.define("Configuration", "Release"),
+            self.define("SkipUWP", "true"),
+        ]
+
+    @property
+    def build_directory(self):
+        solution_path = pathlib.Path(self.pkg.stage.source_path)
+        if self.spec.satsifies("@:67"):
+            solution_path = solution_path / "icu"
+        solution_path = solution_path / "source" / "allinone"
+        return str(solution_path)
+
+    def install(self, pkg, spec, prefix):
+        mkdirp(prefix.lib)
+        mkdirp(prefix.bin)
+        mkdirp(prefix.include)
+        with working_dir(self.pkg.stage.source_path):
+            # install bin
+            install_tree("bin64", prefix.bin)
+            # install lib
+            install_tree("lib64", prefix.lib)
+            # intstall headers
+            install_tree("include", prefix.include)