>>> Emerging (1 of 20) dev-libs/gmp-4.2.1 to /
 * gmp-4.2.1.tar.bz2 MD5 ;-) ...                                          [ ok ]
 * gmp-4.2.1.tar.bz2 RMD160 ;-) ...                                       [ ok ]
 * gmp-4.2.1.tar.bz2 SHA1 ;-) ...                                         [ ok ]
 * gmp-4.2.1.tar.bz2 SHA256 ;-) ...                                       [ ok ]
 * gmp-4.2.1.tar.bz2 size ;-) ...                                         [ ok ]
 * checking ebuild checksums ;-) ...                                      [ ok ]
 * checking auxfile checksums ;-) ...                                     [ ok ]
 * checking miscfile checksums ;-) ...                                    [ ok ]
 * checking gmp-4.2.1.tar.bz2 ;-) ...                                     [ ok ]
>>> Unpacking source...
>>> Unpacking gmp-4.2.1.tar.bz2 to /var/tmp/portage/gmp-4.2.1/work
 * Applying x86-fat.diff ...                                              [ ok ]
 * Applying configure-ppc.diff ...                                        [ ok ]
 * Applying aix.m4-RW.diff ...                                            [ ok ]
 * Applying ia64-popcount.diff ...                                        [ ok ]
 * Applying gmp-4.1.4-noexecstack.patch ...                               [ ok ]
 * Applying gmp-4.2.1-ABI-multilib.patch ...                              [ ok ]
 * Running elibtoolize in: gmp-4.2.1
 *   Applying portage-1.5.10.patch ...
 *   Applying max_cmd_len-1.5.20.patch ...
 *   Applying sed-1.5.6.patch ...
>>> Source unpacked.
>>> Compiling source in /var/tmp/portage/gmp-4.2.1/work/gmp-4.2.1 ...
 * econf: updating gmp-4.2.1/config.guess with /usr/share/gnuconfig/config.guess
 * econf: updating gmp-4.2.1/config.sub with /usr/share/gnuconfig/config.sub
./configure --prefix=/usr --host=i686-pc-linux-gnu --mandir=/usr/share/man --infodir=/usr/share/info --datadir=/usr/share --sysconfdir=/etc --localstatedir=/var/lib --localstatedir=/var/state/gmp --disable-mpfr --disable-mpbsd --enable-cxx --build=i686-pc-linux-gnu
checking build system type... i686-pc-linux-gnu
checking host system type... i686-pc-linux-gnu
checking for a BSD-compatible install... /bin/install -c
checking whether build environment is sane... yes
checking for gawk... gawk
checking whether make sets $(MAKE)... yes
checking whether to enable maintainer-specific portions of Makefiles... no
checking GMPABI=32
checking compiler gcc -march=pentium-m -O2 -pipe -fomit-frame-pointer ... yes
checking compiler gcc -march=pentium-m -O2 -pipe -fomit-frame-pointer has sizeof(long)==4... yes
checking for i686-pc-linux-gnu-gcc... gcc
checking for C compiler default output file name... a.out
checking whether the C compiler works... yes
checking whether we are cross compiling... no
checking for suffix of executables...
checking for suffix of object files... o
checking whether we are using the GNU C compiler... yes
checking whether gcc accepts -g... yes
checking for gcc option to accept ANSI C... none needed
checking how to run the C preprocessor... gcc -E
checking build system compiler gcc... yes
checking for build system preprocessor... gcc -E
checking for build system executable suffix...
checking whether build system compiler is ANSI... yes
checking for build system compiler math library... -lm
checking for i686-pc-linux-gnu-g++... no
checking for i686-pc-linux-gnu-c++... no
checking for i686-pc-linux-gnu-gpp... no
checking for i686-pc-linux-gnu-aCC... no
checking for i686-pc-linux-gnu-CC... no
checking for i686-pc-linux-gnu-cxx... no
checking for i686-pc-linux-gnu-cc++... no
checking for i686-pc-linux-gnu-cl... no
checking for i686-pc-linux-gnu-FCC... no
checking for i686-pc-linux-gnu-KCC... no
checking for i686-pc-linux-gnu-RCC... no
checking for i686-pc-linux-gnu-xlC_r... no
checking for i686-pc-linux-gnu-xlC... no
checking for g++... no
checking for c++... no
checking for gpp... no
checking for aCC... no
checking for CC... no
checking for cxx... no
checking for cc++... no
checking for cl... no
checking for FCC... no
checking for KCC... no
checking for RCC... no
checking for xlC_r... no
checking for xlC... no
checking whether we are using the GNU C++ compiler... no
checking whether g++ accepts -g... no
checking C++ compiler g++  -march=pentium-m -O2 -pipe -fomit-frame-pointer... no
configure: error: C++ compiler not available, see config.log for details

!!! Please attach the following file when filing a report to bugs.gentoo.org:
!!! /var/tmp/portage/gmp-4.2.1/work/gmp-4.2.1/config.log

!!! ERROR: dev-libs/gmp-4.2.1 failed.
Call stack:
  ebuild.sh, line 1546:   Called dyn_compile
  ebuild.sh, line 937:   Called src_compile
  gmp-4.2.1.ebuild, line 42:   Called econf '--localstatedir=/var/state/gmp' '--disable-mpfr' '--disable-mpbsd' '--enable-cxx'
  ebuild.sh, line 540:   Called die

!!! econf failed
!!! If you need support, post the topmost build error, and the call stack if relevant.