[Bug libstdc++/69450] New: [6 Regression] libstdc++-v3/include/math.h:66:1 2: error: 'constexpr bool std::isnan(double)' conflicts with a previous declaration

["danglin at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69450

            Bug ID: 69450
           Summary: [6 Regression] libstdc++-v3/include/math.h:66:1 2:
                    error: 'constexpr bool std::isnan(double)' conflicts
                    with a previous declaration
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: danglin at gcc dot gnu.org
  Target Milestone: ---
              Host: hppa2.0w-hp-hpux11.11
            Target: hppa2.0w-hp-hpux11.11
             Build: hppa2.0w-hp-hpux11.11

/test/gnu/gcc/objdir/./prev-gcc/xg++ -B/test/gnu/gcc/objdir/./prev-gcc/
-B/opt/g
nu/gcc/gcc-6.0/hppa2.0w-hp-hpux11.11/bin/ -nostdinc++
-B/test/gnu/gcc/objdir/prev-hppa2.0w-hp-hpux11.11/libstdc++-v3/src/.libs
-B/test/gnu/gcc/objdir/prev-hppa2
.0w-hp-hpux11.11/libstdc++-v3/libsupc++/.libs 
-I/test/gnu/gcc/objdir/prev-hppa2
.0w-hp-hpux11.11/libstdc++-v3/include/hppa2.0w-hp-hpux11.11 
-I/test/gnu/gcc/objdir/prev-hppa2.0w-hp-hpux11.11/libstdc++-v3/include 
-I/test/gnu/gcc/gcc/libstdc
++-v3/libsupc++
-L/test/gnu/gcc/objdir/prev-hppa2.0w-hp-hpux11.11/libstdc++-v3/s
rc/.libs
-L/test/gnu/gcc/objdir/prev-hppa2.0w-hp-hpux11.11/libstdc++-v3/libsupc+
+/.libs -c   -g -O2 -DIN_GCC     -fno-exceptions -fno-rtti
-fasynchronous-unwind
-tables -W -Wall -Wno-narrowing -Wwrite-strings -Wcast-qual
-Wmissing-format-att
ribute -Woverloaded-virtual -pedantic -Wno-long-long -Wno-variadic-macros
-Wno-o
verlength-strings -Werror -fno-common  -DHAVE_CONFIG_H -DGENERATOR_FILE
-fno-PIE -I. -Ibuild -I../../gcc/gcc -I../../gcc/gcc/build
-I../../gcc/gcc/../include -I./../intl -I../../gcc/gcc/../libcpp/include  \
                -o build/genautomata.o ../../gcc/gcc/genautomata.c
In file included from ../../gcc/gcc/genautomata.c:116:0:
/test/gnu/gcc/objdir/prev-hppa2.0w-hp-hpux11.11/libstdc++-v3/include/math.h:66:1
2: error: 'constexpr bool std::isnan(double)' conflicts with a previous
declarat
ion
 using std::isnan;
            ^~~~~

In file included from
/test/gnu/gcc/objdir/prev-hppa2.0w-hp-hpux11.11/libstdc++-v3/include/cmath:45:0,
                 from
/test/gnu/gcc/objdir/prev-hppa2.0w-hp-hpux11.11/libstdc++-v3/include/math.h:36,
                 from ../../gcc/gcc/genautomata.c:116:
/test/gnu/gcc/objdir/prev-gcc/include-fixed/math.h:129:20: note: previous
declaration 'int isnan(double)'
      extern int    isnan(double);
                    ^~~~~

make[3]: *** [build/genautomata.o] Error 1

This is in stage2.