bpo-31354: Let configure --with-lto work on all builds

Allow configure --with-lto to apply to all builds, not just profile-opt builds.

Whether this is actually useful or not must be determined by the person
building CPython using their own toolchain.

My own quick test on x86_64 Debian 9 (gcc 6.3, binutils 2.28) seemed
to suggest that it wasn't, but I expect better toolchains can or will exist
at some point.  The point is to allow it at all.

Author: octaviansoldea

Makefile.pre.in

@@ -463,7 +463,7 @@ profile-opt:
 	$(MAKE) profile-removal
 
 build_all_generate_profile:
-	$(MAKE) @DEF_MAKE_RULE@ CFLAGS_NODIST="$(CFLAGS) $(PGO_PROF_GEN_FLAG) @LTOFLAGS@" LDFLAGS="$(LDFLAGS) $(PGO_PROF_GEN_FLAG) @LTOFLAGS@" LIBS="$(LIBS)"
+	$(MAKE) @DEF_MAKE_RULE@ CFLAGS_NODIST="$(CFLAGS) $(PGO_PROF_GEN_FLAG)" LDFLAGS="$(LDFLAGS) $(PGO_PROF_GEN_FLAG)" LIBS="$(LIBS)"
 
 run_profile_task:
 	@ # FIXME: can't run for a cross build
@@ -473,7 +473,7 @@ build_all_merge_profile:
 	$(LLVM_PROF_MERGER)
 
 build_all_use_profile:
-	$(MAKE) @DEF_MAKE_RULE@ CFLAGS_NODIST="$(CFLAGS) $(PGO_PROF_USE_FLAG) @LTOFLAGS@" LDFLAGS="$(LDFLAGS) @LTOFLAGS@"
+	$(MAKE) @DEF_MAKE_RULE@ CFLAGS_NODIST="$(CFLAGS) $(PGO_PROF_USE_FLAG)" LDFLAGS="$(LDFLAGS)"
 
 # Compile and run with gcov
 .PHONY=coverage coverage-lcov coverage-report

Misc/NEWS.d/next/Build/2017-09-08-11-48-11.bpo-31354.4f-VJK.rst

@@ -0,0 +1 @@
+Allow --with-lto to be used on all builds, not just `make profile-opt`.

configure

@@ -679,7 +679,6 @@ LLVM_PROF_FILE
 LLVM_PROF_MERGER
 PGO_PROF_USE_FLAG
 PGO_PROF_GEN_FLAG
-LTOFLAGS
 DEF_MAKE_RULE
 DEF_MAKE_ALL_RULE
 ABIFLAGS
@@ -1511,8 +1510,8 @@ Optional Packages:
   --with-suffix=.exe      set executable suffix
   --with-pydebug          build with Py_DEBUG defined
   --with-assertions       build with C assertions enabled
-  --with-lto              Enable Link Time Optimization in PGO builds.
-                          Disabled by default.
+  --with-lto              Enable Link Time Optimization in any build. Disabled
+                          by default.
   --with-hash-algorithm=[fnv|siphash24]
                           select hash algorithm
   --with-address-sanitizer
@@ -6511,7 +6510,6 @@ else
 fi
 
 # Enable LTO flags
-
 { $as_echo "$as_me:${as_lineno-$LINENO}: checking for --with-lto" >&5
 $as_echo_n "checking for --with-lto... " >&6; }
 
@@ -6557,6 +6555,8 @@ if test "$Py_LTO" = 'true' ; then
       esac
       ;;
   esac
+  CFLAGS="$CFLAGS $LTOFLAGS"
+  LDFLAGS="$LDFLAGS $LTOFLAGS"
 fi
 
 # Enable PGO flags.

configure.ac

@@ -1282,9 +1282,8 @@ else
 fi
 
 # Enable LTO flags
-AC_SUBST(LTOFLAGS)
 AC_MSG_CHECKING(for --with-lto)
-AC_ARG_WITH(lto, AS_HELP_STRING([--with-lto], [Enable Link Time Optimization in PGO builds. Disabled by default.]),
+AC_ARG_WITH(lto, AS_HELP_STRING([--with-lto], [Enable Link Time Optimization in any build. Disabled by default.]),
 [
 if test "$withval" != no
 then
@@ -1319,6 +1318,8 @@ if test "$Py_LTO" = 'true' ; then
       esac
       ;;
   esac
+  CFLAGS="$CFLAGS $LTOFLAGS"
+  LDFLAGS="$LDFLAGS $LTOFLAGS"
 fi
 
 # Enable PGO flags.