marzer.tomlplusplus: no SSE2 path under the MSVC ABI (revision 2) (#575)

* marzer.tomlplusplus: the module unit builds toml++ without its SSE2 path (revision 2)

<emmintrin.h> defines its intrinsics static inline. Under the MSVC ABI clang
gives such a function the same mangled name in every module whose global
module fragment includes the header, so a unit that imports both std (MSVC's
library includes the intrinsics) and tomlplusplus fails with "definition with
same mangled name '?_mm_movemask_epi8@@...'". toml++ used SSE2 only to skip
ASCII faster; with TOML_ENABLE_SIMD 0 the scalar path parses the same
documents and the module includes no intrinsics header.

* marzer.tomlplusplus: turn SSE2 off under the MSVC ABI only (_MSC_VER)

The collision is an MSVC-ABI one; Linux, macOS and MinGW keep toml++'s SSE2
path.

Author: Sunrisepeak

pkgs/m/marzer.tomlplusplus.lua

@@ -53,7 +53,8 @@ package = {
                 },
                 sha256 = "8517f65938a4faae9ccf8ebb36631a38c1cadfb5efa85d9a72e15b9e97d25155",
                 -- 1: Form B -> Form A (install() writes mcpp.toml + the module unit).
-                revision = 1,
+                -- 2: under the MSVC ABI the module unit builds toml++ without its SSE2 path.
+                revision = 2,
             },
         },
         macosx = {
@@ -64,7 +65,8 @@ package = {
                 },
                 sha256 = "8517f65938a4faae9ccf8ebb36631a38c1cadfb5efa85d9a72e15b9e97d25155",
                 -- 1: Form B -> Form A (install() writes mcpp.toml + the module unit).
-                revision = 1,
+                -- 2: under the MSVC ABI the module unit builds toml++ without its SSE2 path.
+                revision = 2,
             },
         },
         windows = {
@@ -75,7 +77,8 @@ package = {
                 },
                 sha256 = "8517f65938a4faae9ccf8ebb36631a38c1cadfb5efa85d9a72e15b9e97d25155",
                 -- 1: Form B -> Form A (install() writes mcpp.toml + the module unit).
-                revision = 1,
+                -- 2: under the MSVC ABI the module unit builds toml++ without its SSE2 path.
+                revision = 2,
             },
         },
     },
@@ -122,6 +125,16 @@ local MODULE_UNIT = [==[
 module;
 
 #define TOML_UNDEF_MACROS 0
+// Under the MSVC ABI (cl, or clang in MSVC mode: both define _MSC_VER),
+// no SSE2 path: <emmintrin.h> defines its intrinsics `static inline`, and
+// clang gives such a function the same mangled name in every module whose
+// global module fragment includes it — a unit importing both `std` (MSVC's
+// library includes the intrinsics) and `tomlplusplus` then fails with
+// "definition with same mangled name". Elsewhere SSE2 stays on. toml++ uses
+// it only to skip ASCII faster; the scalar path parses the same documents.
+#if defined(_MSC_VER)
+#define TOML_ENABLE_SIMD 0
+#endif
 // mcpp#797: a host-module compile is not given this package's include_dirs,
 // so reach the header relative to this file (src/modules/ -> include/).
 // Same file either way; restore `<toml++/toml.hpp>` once mcpp#797 is settled.