[root-config] Put the C++ version into auxcflags by default.

The C++ version flag should be needed on all linux/mac, but it was
missing e.g. for RISC-V. To remedy that, the flags is now set by
default, and only overridden when needed.

See also:
https://root-forum.cern.ch/t/no-auxcflags-set-in-root-config-when-building-for-riscv64-6-36-02/64163

Author: hageboeck

config/root-config.in

@@ -151,6 +151,7 @@ fi
 
 # Set the C++ standard version
 cxxversionflag="@configstd@ "
+auxcflags="${cxxversionflag} "
 
 case $arch in
 aix5)
@@ -163,98 +164,95 @@ aix5)
    ;;
 aixgcc)
    # IBM AIX with g++
-   auxcflags="${cxxversionflag} -fsigned-char -fsized-deallocation"
+   auxcflags+="-fsigned-char -fsized-deallocation"
    auxlibs=
    #forcelibs=$rootulibs
    #forceglibs=$rootuglibs
    #forceevelibs=$rootuevelibs
    ;;
 solarisgcc)
    # Solaris g++ 2.8.x
-   auxcflags="${cxxversionflag}"
    auxlibs="-L/usr/ccs/lib -lm -lsocket -lgen -ldl"
    ;;
 solarisCC5)
    # Solaris CC 5.0
    if [ `uname -p` = "i386" ]; then
-      auxcflags="${cxxversionflag} -library=stlport4"
+      auxcflags+="-library=stlport4"
       auxldflags="-library=stlport4"
    else
-      auxcflags="${cxxversionflag}"
       auxldflags=
    fi
    auxlibs="-lm -ldl -lnsl -lsocket"
    ;;
 solaris64CC5)
    # Solaris CC 5.0 x86-64
-   auxcflags="${cxxversionflag} -m64 -library=stlport4"
+   auxcflags+="-m64 -library=stlport4"
    auxldflags="-m64 -library=stlport4"
    auxlibs="-lm -ldl -lnsl -lsocket"
    ;;
 linux)
    # Linux with gcc >= 3.x
-   auxcflags="${cxxversionflag} -m32 -msse -mfpmath=sse -fsized-deallocation"
+   auxcflags+="-m32 -msse -mfpmath=sse -fsized-deallocation"
    auxldflags="-m32 -msse -mfpmath=sse "
    auxlibs="-lm -ldl -rdynamic"
    ;;
 linuxicc)
    # Linux with the Intel icc compiler
-   auxcflags="${cxxversionflag} -fsized-deallocation"
+   auxcflags+="-fsized-deallocation"
    auxlibs="-limf -lm -ldl"
    ;;
 linuxppcgcc)
    # PPC Linux with gcc
-   auxcflags="${cxxversionflag} -m32 -fsigned-char -fsized-deallocation"
+   auxcflags+="-m32 -fsigned-char -fsized-deallocation"
    auxldflags="-m32"
    auxlibs="-lm -ldl -rdynamic"
    ;;
 linuxppc64gcc)
    # PPC64/PPC64LE (64 bit mode) Linux with gcc
-   auxcflags="${cxxversionflag} -m64 -fsigned-char -fsized-deallocation"
+   auxcflags+="-m64 -fsigned-char -fsized-deallocation"
    auxldflags="-m64"
    auxlibs="-lm -ldl -rdynamic"
    ;;
 linuxx8664gcc)
    # AMD Opteron and Intel EM64T (64 bit mode) Linux with gcc 3.x
-   auxcflags="${cxxversionflag} -m64 -fsized-deallocation"
+   auxcflags+="-m64 -fsized-deallocation"
    auxldflags="-m64"
    auxlibs="-lm -ldl -rdynamic"
    ;;
 linuxx8664icc)
    # AMD Opteron and Intel EM64T (64 bit mode) Linux with Intel icc
-   auxcflags="${cxxversionflag}"
    auxlibs="-limf -lm -ldl"
    ;;
 linuxx8664k1omicc)
    # Intel Many Integrated Cores Architecture (Knights Corner) Linux with Intel icc
-   auxcflags="${cxxversionflag} -mmic -I/usr/include"
+   auxcflags+="-mmic -I/usr/include"
    auxlibs="-limf -lm -ldl"
    ;;
 linuxx32gcc)
    # x32 ABI (64 bit mode with 32 bit pointers) Linux with gcc > 4.7
-   auxcflags="${cxxversionflag} -mx32 -fsized-deallocation"
+   auxcflags+="-mx32 -fsized-deallocation"
    auxldflags="-mx32"
    auxlibs="-lm -ldl -rdynamic"
    ;;
 linuxarm)
    # ARM Linux with gcc
-   auxcflags="${cxxversionflag} -fsigned-char -fsized-deallocation"
+   auxcflags+="-fsigned-char -fsized-deallocation"
    auxlibs="-lm -ldl -rdynamic"
    ;;
 linuxarm64)
    # ARMv8-A (AArch64) Linux with gcc
-   auxcflags="${cxxversionflag} -fsigned-char -fsized-deallocation"
+   auxcflags+="-fsigned-char -fsized-deallocation"
    auxlibs="-lm -ldl -rdynamic"
    ;;
 linuxs390gcc)
    # s390 (31 bit mode) Linux with gcc
-   auxcflags="${cxxversionflag} -m31 -fsigned-char -fsized-deallocation"
+   auxcflags+="-m31 -fsigned-char -fsized-deallocation"
    auxldflags="-m31"
    auxlibs="-lm -ldl -rdynamic"
    ;;
 linuxs390xgcc)
    # s390x (64 bit mode) Linux with gcc
-   auxcflags="${cxxversionflag} -m64 -fsigned-char -fsized-deallocation"
+   auxcflags+="-m64 -fsigned-char -fsized-deallocation"
    auxldflags="-m64"
    auxlibs="-lm -ldl -rdynamic"
    ;;
@@ -268,22 +266,19 @@ linuxloong64)
    ;;
 freebsd*)
    # FreeBSD
-   auxcflags="${cxxversionflag}"
    auxlibs="-lm"
    ;;
 openbsd)
    # OpenBSD with libc
-   auxcflags="${cxxversionflag}"
    auxlibs="-lm -lstdc++"
    ;;
 macosxicc)
    # MacOS X with Intel icc compiler
-   auxcflags="${cxxversionflag}"
    auxlibs="-lm -ldl"
    ;;
 macosx64|macosxarm64)
    # MacOS X with gcc (GNU cc v4.x) in 64 bit mode
-   auxcflags="${cxxversionflag} -m64"
+   auxcflags+="-m64"
    auxldflags="-m64"
    auxlibs="-lm -ldl"
    ;;