* Fix "bootstrap.bat borland" failing to find label "Test_Path"
If an override toolset is given in the `bootstrap.bat` command-line,
`bootstrap.bat` -> `src/engine/build.bat` bypasses loading
`src/engine/guess_toolset.bat` entirely. Later on the call to
`Test_Path` from `build.bat` -> `config_toolset.bat` fails to find that
label.
Fix this by making a new parameterized entry-point `test_path` inside
`guess_toolset.bat` for this caller in `config_toolset.bat`.
Fixes: #382.
* Handle spaces in C++Builder toolchain path
Nowadays a default installation goes into %PROGRAMFILES%, e.g.
"C:\Program Files (x86)\Embarcadero\Studio\20.0\Bin".
* Add "-Nd" before "/D"-options for bcc32.exe
The preprocessor of the old Borland/C++Builder compiler (bcc32.exe) by
default does not accept preprocessor statements of the form:
#if SYMBOL_NAME
where `SYMBOL_NAME` was `#define`-ed without a value. It insists on the
`#if defined(SYMBOL_NAME)` or `#ifdef SYMBOL_NAME` forms (emitting error
E2188 "expression syntax"). The workaround is to specify the `-Nd`
option before the offending `/D` options, which effectively provides a
value of "1" to the symbols being #define-ed. Apply this workaround in
the recipes of `bjam` and `b2` to satisfy the preprocessor.
The alternative here would be to migrate to the Clang-based (and much
more standard-compliant) bcc32c.exe, but that would be a more involved
change.
* Separate :Guess_Yacc logic from :Guess_Toolset in build.bat
This was an existing benign issue introduced in 00c2358, but it became
apparent after 9339693.
* Fixed `build.bat` stack overflow on some machines by splitting up to several files
* CSharp script simplified and now will check VC++ toolset version
