bpo-45433: Do not link libpython against libcrypt (GH-28881)

Save/restore LIBS when calling AC_SEARCH_LIBS(..., crypt). This avoid
linking libpython with libcrypt.

Doc/whatsnew/3.11.rst

@@ -457,6 +457,8 @@ Build Changes
 * CPython can now be built with the ThinLTO option via ``--with-lto=thin``.
   (Contributed by Dong-hee Na and Brett Holman in :issue:`44340`.)
 
+* libpython is no longer linked against libcrypt.
+  (Contributed by Mike Gilbert in :issue:`45433`.)
 
 C API Changes
 =============

Misc/NEWS.d/next/Build/2021-10-11-16-08-37.bpo-45433.pVDkMV.rst

@@ -0,0 +1 @@
+Avoid linking libpython with libcrypt.

configure

@@ -13227,6 +13227,8 @@ done
 
 # We search for both crypt and crypt_r as one or the other may be defined
 # This gets us our -lcrypt in LIBS when required on the target platform.
+# Save/restore LIBS to avoid linking libpython with libcrypt.
+LIBS_SAVE=$LIBS
 { $as_echo "$as_me:${as_lineno-$LINENO}: checking for library containing crypt" >&5
 $as_echo_n "checking for library containing crypt... " >&6; }
 if ${ac_cv_search_crypt+:} false; then :
@@ -13368,6 +13370,7 @@ rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
 
 fi
 
+LIBS=$LIBS_SAVE
 
 for ac_func in clock_gettime
 do :

configure.ac

@@ -4085,6 +4085,8 @@ AC_CHECK_FUNCS(setpgrp,
 
 # We search for both crypt and crypt_r as one or the other may be defined
 # This gets us our -lcrypt in LIBS when required on the target platform.
+# Save/restore LIBS to avoid linking libpython with libcrypt.
+LIBS_SAVE=$LIBS
 AC_SEARCH_LIBS(crypt, crypt)
 AC_SEARCH_LIBS(crypt_r, crypt)
 
@@ -4099,6 +4101,7 @@ char *r = crypt_r("", "", &d);
     [AC_DEFINE(HAVE_CRYPT_R, 1, [Define if you have the crypt_r() function.])],
     [])
 )
+LIBS=$LIBS_SAVE
 
 AC_CHECK_FUNCS(clock_gettime, [], [
     AC_CHECK_LIB(rt, clock_gettime, [