Add CMake project, GCC support (#540)

This is extract from #211 that enables compilation with GCC. With #211
now in the state of bitrot, I would rather try approaching it in smaller
steps that can be hopefully merged quicker, even if it does not provide
full support for all the features #211 provided.

This will _compile_ correctly with my (@janisozaur) GCC, but clang is
more picky about flexible array members and refuses to compile it yet.
I will extract remaining parts of #211 in future PRs.

I marked @fwcd as author, as he did most of the work in #211.

src/CalcManager/Ratpack/CMakeLists.txt

@@ -0,0 +1,14 @@
+target_sources(CalcManager PRIVATE
+	basex.cpp
+	conv.cpp
+	exp.cpp
+	fact.cpp
+	itrans.cpp
+	itransh.cpp
+	logic.cpp
+	num.cpp
+	rat.cpp
+	support.cpp
+	trans.cpp
+	transh.cpp
+)

src/CalcManager/Ratpack/conv.cpp

@@ -18,7 +18,7 @@
 //---------------------------------------------------------------------------
 
 #include <algorithm>
-#include <winerror.h>
+#include "winerror_cross_platform.h"
 #include <sstream>
 #include <cstring> // for memmove, memcpy
 #include "ratpak.h"

src/CalcManager/Ratpack/ratpak.h

@@ -21,7 +21,7 @@
 #include <string>
 #include "CalcErr.h"
 #include <cstring> // for memmove
-#include <sal.h>   // for SAL
+#include "sal_cross_platform.h"   // for SAL
 
 static constexpr uint32_t BASEXPWR = 31L;     // Internal log2(BASEX)
 static constexpr uint32_t BASEX = 0x80000000; // Internal radix used in calculations, hope to raise