unix: link _decimal against standalone libmpdec

The previous commit enabled support for building mpdecimal as a
standalone project. This commit replaces the inline build of
mpdecimal as part of CPython to linking against our standalone
mpdecimal.

On Python 3.8 and 3.9, this effectively upgrades mpdecimal to 2.5.1.
This required a minimal patch.

As part of this, we also fix the defines on macOS. UNIVERSAL is no
longer needed, as this is handled by mpdecimal's build system. But
_decimal.c does need one of the CONFIG_ defines set or else things
blow up.

Author: indygreg

cpython-unix/build-cpython.sh

@@ -188,6 +188,11 @@ patch -p1 < ${ROOT}/patch-ctypes-callproc.patch
 # See https://bugs.python.org/issue37060.
 patch -p1 < ${ROOT}/patch-ctypes-static-binary.patch
 
+# Older versions of Python need patching to work with modern mpdecimal.
+if [[ "${PYTHON_MAJMIN_VERSION}" = "3.8" || "${PYTHON_MAJMIN_VERSION}" = "3.9" ]]; then
+    patch -p1 < ${ROOT}/patch-decimal-modern-mpdecimal.patch
+fi
+
 # CPython 3.10 added proper support for building against libedit outside of
 # macOS. On older versions, we need to patch readline.c.
 if [[ "${PYTHON_MAJMIN_VERSION}" = "3.8" || "${PYTHON_MAJMIN_VERSION}" = "3.9" ]]; then
@@ -262,6 +267,7 @@ CONFIGURE_FLAGS="
     --host=${TARGET_TRIPLE}
     --prefix=/install
     --with-openssl=${TOOLS_PATH}/deps
+    --with-system-libmpdec
     --without-ensurepip
     ${EXTRA_CONFIGURE_FLAGS}"
 

cpython-unix/extension-modules.yml

@@ -211,59 +211,22 @@ _dbm:
 _decimal:
   sources:
     - _decimal/_decimal.c
-    - _decimal/libmpdec/basearith.c
-    - _decimal/libmpdec/constants.c
-    - _decimal/libmpdec/context.c
-    - _decimal/libmpdec/convolute.c
-    - _decimal/libmpdec/crt.c
-    - _decimal/libmpdec/difradix2.c
-    - _decimal/libmpdec/fnt.c
-    - _decimal/libmpdec/fourstep.c
-    - _decimal/libmpdec/io.c
-    - _decimal/libmpdec/mpdecimal.c
-    - _decimal/libmpdec/numbertheory.c
-    - _decimal/libmpdec/sixstep.c
-    - _decimal/libmpdec/transpose.c
-  sources-conditional:
-    # memory.c renamed to mpalloc.c in 3.9.
-    - source: _decimal/libmpdec/memory.c
-      maximum-python-version: "3.8"
-    - source: _decimal/libmpdec/mpalloc.c
-      minimum-python-version: "3.9"
-  includes:
-    - Modules/_decimal/libmpdec
+  includes-deps:
+    - include
   defines-conditional:
-    - define: ANSI=1
-      targets:
-        - .*-unknown-linux-.*
-    - define: ASM=1
-      targets:
-        - i686-.*
-        - x86_64.*
     - define: CONFIG_32=1
       targets:
         - armv7-.*
         - i686-.*
         - mips-.*
         - mipsel-.*
     - define: CONFIG_64=1
-      targets:
-        # CONFIG_64 is mutually exclusive with UNIVERSAL=1
-        - aarch64-unknown-linux-.*
-        - s390x-unknown-linux-.*
-        - x86_64.*-unknown-linux-.*
-    - define: HAVE_UINT128_T=1
       targets:
         - aarch64-.*
-        - s390x-.*
+        - s390x-unknown-linux-.*
         - x86_64.*
-    - define: PPRO=1
-      targets:
-        - i686-.*
-    # TODO is this correct for non-universal binaries?
-    - define: UNIVERSAL=1
-      targets:
-        - .*-apple-.*
+  links:
+    - mpdec
 
 _elementtree:
   sources:

cpython-unix/patch-decimal-modern-mpdecimal.patch

@@ -0,0 +1,22 @@
+diff --git a/Modules/_decimal/_decimal.c b/Modules/_decimal/_decimal.c
+index 83e237d02b..9a4329f494 100644
+--- a/Modules/_decimal/_decimal.c
++++ b/Modules/_decimal/_decimal.c
+@@ -3293,7 +3293,7 @@ dec_format(PyObject *dec, PyObject *args)
+     }
+     else {
+         size_t n = strlen(spec.dot);
+-        if (n > 1 || (n == 1 && !isascii((uchar)spec.dot[0]))) {
++        if (n > 1 || (n == 1 && !isascii((unsigned char)spec.dot[0]))) {
+             /* fix locale dependent non-ascii characters */
+             dot = dotsep_as_utf8(spec.dot);
+             if (dot == NULL) {
+@@ -3302,7 +3302,7 @@ dec_format(PyObject *dec, PyObject *args)
+             spec.dot = PyBytes_AS_STRING(dot);
+         }
+         n = strlen(spec.sep);
+-        if (n > 1 || (n == 1 && !isascii((uchar)spec.sep[0]))) {
++        if (n > 1 || (n == 1 && !isascii((unsigned char)spec.sep[0]))) {
+             /* fix locale dependent non-ascii characters */
+             sep = dotsep_as_utf8(spec.sep);
+             if (sep == NULL) {