title: Why would g++ be unable to find system includes which are installed?
body: <p>Here's a simple example program which compiles on my desktop linux machine (Ubuntu 14.04 64 bit intel, fwiw):  </p>
  
  <pre><code>#include &lt;iostream&gt;
  #include &lt;cmath&gt;
  
  using namespace std;
  
  int main(){
    cout&lt;&lt;"hello"&lt;&lt;endl;
    return 0;
  }
  </code></pre>
  
  <p>When I try to compile it on an embedded machine which appears to have the header files (and the equivalent of build-essential) installed:  </p>
  
  <pre><code>me@t4240rdb:~$ ls /usr/include/c++/4.9.2/iostream
  /usr/include/c++/4.9.2/iostream
  me@t4240rdb:~# find /usr/include/ -name cmath
  /usr/include/c++/4.9.2/ext/cmath
  /usr/include/c++/4.9.2/cmath
  /usr/include/c++/4.9.2/tr1/cmath
  </code></pre>
  
  <p>using <code>g++ /home/me/tc.cpp</code>, I get  </p>
  
  <pre><code>/home/me/tc.cpp:1:20: fatal error: iostream: No such file or directory
   #include &lt;iostream&gt;
                      ^
  compilation terminated.
  </code></pre>
  
  <p>Anyone have any idea why this would happen?  </p>
  
  <p>Including the output of g++ -v as requested in the comments:</p>
  
  <pre><code>me@t4240rdb:~# g++ -v /home/me/tc.cpp 
  Using built-in specs.
  COLLECT_GCC=g++
  COLLECT_LTO_WRAPPER=/usr/lib64/gcc/gcc/powerpc64-fsl-linux/4.9.2/lto-wrapper
  Target: powerpc64-fsl-linux
  Configured with: /home/jenkins/ci/iso-make/master/b4860qds-64b/build_b4860qds-64b/tmp/work-shared/gcc-4.9.2-r0/gcc-4.9.2/configure --build=x86_64-linux --host=powerpc64-fsl-linux --target=powerpc64-fsl-linux --prefix=/usr --exec_prefix=/usr --bindir=/usr/bin --sbindir=/usr/sbin --libexecdir=/usr/lib64/gcc --datadir=/usr/share --sysconfdir=/etc --sharedstatedir=/com --localstatedir=/var --libdir=/usr/lib64 --includedir=/usr/include --oldincludedir=/usr/include --infodir=/usr/share/info --mandir=/usr/share/man --disable-silent-rules --disable-dependency-tracking --with-libtool-sysroot=/home/jenkins/ci/iso-make/master/b4860qds-64b/build_b4860qds-64b/tmp/sysroots/b4860qds-64b --with-gnu-ld --enable-shared --enable-languages=c,c++ --enable-threads=posix --enable-multilib --enable-c99 --enable-long-long --enable-symvers=gnu --enable-libstdcxx-pch --program-prefix=powerpc64-fsl-linux- --without-local-prefix --enable-target-optspace --enable-lto --enable-libssp --disable-bootstrap --disable-libmudflap --with-system-zlib --with-linker-hash-style=gnu --enable-linker-build-id --with-ppl=no --enable-checking=release --enable-cheaders=c_global --with-sysroot=/ --with-build-sysroot=/home/jenkins/ci/iso-make/master/b4860qds-64b/build_b4860qds-64b/tmp/sysroots/b4860qds-64b --with-native-system-header-dir=/home/jenkins/ci/iso-make/master/b4860qds-64b/build_b4860qds-64b/tmp/sysroots/b4860qds-64b/usr/include --with-gxx-include-dir=/usr/include/c++/4.9.2 --with-long-double-128 --enable-nls --enable-__cxa_atexit
  Thread model: posix
  gcc version 4.9.2 (GCC) 
  COLLECT_GCC_OPTIONS='-v' '-shared-libgcc'
   /usr/lib64/gcc/gcc/powerpc64-fsl-linux/4.9.2/cc1plus -quiet -v -D_GNU_SOURCE -D__unix__ -D__gnu_linux__ -D__linux__ -Dunix -D__unix -Dlinux -D__linux -Asystem=linux -Asystem=unix -Asystem=posix /home/me/tc.cpp -quiet -dumpbase tc.cpp -auxbase tc -version -o /tmp/cc4avGfH.s
  GNU C++ (GCC) version 4.9.2 (powerpc64-fsl-linux)
      compiled by GNU C version 4.9.2, GMP version 6.0.0, MPFR version 3.1.2, MPC version 1.0.2
  GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
  ignoring nonexistent directory "usr/include/c++/4.9.2"
  ignoring nonexistent directory "usr/include/c++/4.9.2/powerpc64-fsl-linux"
  ignoring nonexistent directory "usr/include/c++/4.9.2/backward"
  ignoring nonexistent directory "/usr/local/include"
  ignoring nonexistent directory "/usr/lib64/gcc/powerpc64-fsl-linux/4.9.2/../../../../powerpc64-fsl-linux/include"
  #include "..." search starts here:
  #include &lt;...&gt; search starts here:
   /usr/lib64/gcc/powerpc64-fsl-linux/4.9.2/include
   /usr/lib64/gcc/powerpc64-fsl-linux/4.9.2/include-fixed
   /usr/include
  End of search list.
  GNU C++ (GCC) version 4.9.2 (powerpc64-fsl-linux)
      compiled by GNU C version 4.9.2, GMP version 6.0.0, MPFR version 3.1.2, MPC version 1.0.2
  GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
  Compiler executable checksum: 63db6eac369c397424f29967693724f9
  /home/me/tc.cpp:1:20: fatal error: iostream: No such file or directory
   #include &lt;iostream&gt;
                      ^
  compilation terminated.
  </code></pre>
  
  <p>It's quite interesting -- there's clearly something wrong with the configuration.  How do I fix it?  </p>