Drop support for building with old Visual Studio versions

[cmb69]

The first commit requires users to have at least Visual Studio 2015; the second commit raises that to Visual Studio 2017 RTW; the third commit even raises that to Visual Studio 2019 RTW 16.0.

Note that building with Visual Studio 2017 15.9.64 (latest version) fails on

php-src/ext/bcmath/libbcmath/src/convert.h

Line 22 in d100caa

char *bc_copy_and_toggle_bcd(char *restrict dest, const char *source, const char *source_end);

because the restrict keyword is not supported. Thus, if we still want to support Visual Studio 2017, we would need to fix this (and maybe more; I haven't done a full snapshot build).

However, I think we should (or even need to) raise the bar even further. Builds with Visual Studio 2019 16.11.38 (latest version) appear to work flawlessly, but I'm not sure whether somewhat older Visual Studio 2019 versions would work (and I don't think I can test this since going back to older Visual Studio 2019 version is impossible, to my knowledge; you don't need to update, but you can't install an older version).

For details regarding the versioning details, see https://learn.microsoft.com/en-us/cpp/overview/compiler-versions?view=msvc-170.

[Girgias]

This makes sense to me

[cmb69]

Oh, just noticed that I forgot to clean up toolset_get_compiler_name():

php-src/win32/build/confutils.js

Lines 3107 to 3125 in 794ba29

	if (version >= 1950) {
	return name;
	} else if (version >= 1930) {
	name = short ? "VS17" : "Visual C++ 2022";
	} else if (version >= 1920) {
	/* NOTE - VS is intentional. Due to changes in recent Visual Studio
	versioning scheme referring to the exact VC++ version is
	hardly predictable. From this version on, it refers to
	Visual Studio version and implies the default toolset.
	When new versions are introduced, adapt also checks in
	php_win32_image_compatible(), if needed. */
	name = short ? "VS16" : "Visual C++ 2019";
	} else if (version >= 1910) {
	name = short ? "VC15" : "Visual C++ 2017";
	} else if (version >= 1900) {
	name = short ? "VC14" : "Visual C++ 2015";
	} else {
	ERROR("Unsupported Visual C++ compiler " + version);
	}

There might be more. I'll have a closer look.

[cmb69]

Indeed, need to check all _MSC_VER uses in the sources.

[cmb69]

Indeed, need to check all _MSC_VER uses in the sources.

D'oh! That opens up a can of worms, and is probably better adressed on its own (probably multiple PRs).