[PATCH] libstdc++: Allow 'configure.host' to modify 'EXTRA_CFLAGS', 'EXTRA_CXX_FLAGS'

[Thomas Schwinge]

In particular, 'GLIBCXX_ENABLE_CXX_FLAGS' shouldn't overwrite 'EXTRA_CXX_FLAGS'
(and prepend any additional '--enable-cxx-flags=[...]').

	libstdc++-v3/
	* acinclude.m4 (GLIBCXX_ENABLE_CXX_FLAGS): Prepend any additional
	flags to 'EXTRA_CXX_FLAGS'.
	* configure: Regenerate.
	* configure.host: Document 'EXTRA_CFLAGS', 'EXTRA_CXX_FLAGS'.
---
 libstdc++-v3/acinclude.m4   | 3 ++-
 libstdc++-v3/configure      | 3 ++-
 libstdc++-v3/configure.host | 4 ++++
 3 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/libstdc++-v3/acinclude.m4 b/libstdc++-v3/acinclude.m4
index b3423d7957a..3287dab3b89 100644
--- a/libstdc++-v3/acinclude.m4
+++ b/libstdc++-v3/acinclude.m4
@@ -3269,7 +3269,8 @@ AC_DEFUN([GLIBCXX_ENABLE_CXX_FLAGS], [dnl
     done
   fi
 
-  EXTRA_CXX_FLAGS="$enable_cxx_flags"
+  # Prepend the additional flags.
+  EXTRA_CXX_FLAGS="$enable_cxx_flags $EXTRA_CXX_FLAGS"
   AC_MSG_RESULT($EXTRA_CXX_FLAGS)
   AC_SUBST(EXTRA_CXX_FLAGS)
 ])
diff --git a/libstdc++-v3/configure b/libstdc++-v3/configure
index e115ee55739..ba908577a66 100755
--- a/libstdc++-v3/configure
+++ b/libstdc++-v3/configure
@@ -19452,7 +19452,8 @@ fi
     done
   fi
 
-  EXTRA_CXX_FLAGS="$enable_cxx_flags"
+  # Prepend the additional flags.
+  EXTRA_CXX_FLAGS="$enable_cxx_flags $EXTRA_CXX_FLAGS"
   { $as_echo "$as_me:${as_lineno-$LINENO}: result: $EXTRA_CXX_FLAGS" >&5
 $as_echo "$EXTRA_CXX_FLAGS" >&6; }
 
diff --git a/libstdc++-v3/configure.host b/libstdc++-v3/configure.host
index 45f55b250ce..1e84c78af30 100644
--- a/libstdc++-v3/configure.host
+++ b/libstdc++-v3/configure.host
@@ -61,6 +61,10 @@
 #
 # It possibly modifies the following variables:
 #
+#   EXTRA_CFLAGS           extra flags to pass when compiling C code
+#
+#   EXTRA_CXX_FLAGS        extra flags to pass when compiling C++ code
+#
 #   OPT_LDFLAGS            extra flags to pass when linking the library, of
 #                          the form '-Wl,blah'
 #                          (defaults to empty in acinclude.m4)
-- 
2.34.1