tidy-up: OS names

Use these words and casing more consistently across text, comments and
one curl tool output:
AIX, ALPN, ANSI, BSD, Cygwin, Darwin, FreeBSD, GitHub, HP-UX, Linux,
macOS, MS-DOS, MSYS, MinGW, NTLM, POSIX, Solaris, UNIX, Unix, Unicode,
WINE, WebDAV, Win32, winbind, WinIDN, Windows, Windows CE, Winsock.

Mostly OS names and a few more.

Also a couple of other minor text fixups.

Closes #14360

projects/wolfssl_options.h

@@ -29,7 +29,7 @@ build-wolfssl will copy to the wolfSSL include directories and will result in
 maximum compatibility.
 
 These are the configure options that were used to build wolfSSL v5.1.1 in
-mingw and generate the options in this file:
+MinGW and generate the options in this file:
 
 C_EXTRA_FLAGS="\
   -Wno-attributes \

projects/wolfssl_override.props

@@ -16,7 +16,7 @@ file by using the CustomAfterMicrosoftCommonTargets property.
       -->
       <ForcedIncludeFiles>$(SolutionDir)\wolfssl\options.h;%(ForcedIncludeFiles);</ForcedIncludeFiles>
       <!--
-      Do not use the Unicode character set since their mingw config doesn't.
+      Do not use the Unicode character set since their MinGW config does not.
       Do not use their IDE\WIN\user_settings.h since we have wolfssl_options.h.
       -->
       <UndefinePreprocessorDefinitions>_UNICODE;UNICODE;WOLFSSL_USER_SETTINGS;CYASSL_USER_SETTINGS;%(UndefinePreprocessorDefinitions);</UndefinePreprocessorDefinitions>