libtool fails without a CXX compiler installed

[Eric Sandall]

(Example is from compiling pkgconfig):

Without g++ installed:
checking whether we are using the GNU C++ compiler... no
checking whether g++ accepts -g... no
checking dependency style of g++... none
checking how to run the C++ preprocessor... /lib/cpp
configure: error: C++ preprocessor "/lib/cpp" fails sanity check
See `config.log' for more details

config.log:
...
configure:4894: /lib/cpp  conftest.cc
cpp: conftest.cc: C++ compiler not installed on this system
configure:4900: $? = 1
...

Compiles fine with g++ installed.

However, when I check the compile log it never calls g++, just checks
for its
existence and fails out.

(References: http://bugs.sourcemage.org/show_bug.cgi?id=8957 and
https://bugs.freedesktop.org/show_bug.cgi?id=3376).