Checking if your kit is complete...
Looks good
Writing Makefile for JSON::XS
cp XS.pm blib/lib/JSON/XS.pm
cp XS/Boolean.pm blib/lib/JSON/XS/Boolean.pm
/home/cpanrun/build/5.6.1/bin/perl -I/home/cpanrun/build/5.6.1/lib/5.6.1/i686-linux-thread-multi -I/home/cpanrun/build/5.6.1/lib/5.6.1 /home/cpanrun/build/5.6.1/lib/5.6.1/ExtUtils/xsubpp  -typemap /home/cpanrun/build/5.6.1/lib/5.6.1/ExtUtils/typemap -typemap typemap XS.xs > XS.xsc && mv XS.xsc XS.c
gcc -c  -DUSE_REENTRANT_API -D_GNU_SOURCE -D_REENTRANT -fno-strict-aliasing -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64 -O2   -DVERSION=\"1.5\" -DXS_VERSION=\"1.5\" -fpic -I/home/cpanrun/build/5.6.1/lib/5.6.1/i686-linux-thread-multi/CORE  XS.c
In file included from XS.xs:5:
/usr/include/assert.h:79: warning: `assert' redefined
/home/cpanrun/build/5.6.1/lib/5.6.1/i686-linux-thread-multi/CORE/perl.h:2191: warning: this is the location of the previous definition
XS.xs: In function `encode_str':
XS.xs:255: warning: assignment makes pointer from integer without a cast
XS.xs: In function `decode_num':
XS.xs:1015: `IS_NUMBER_IN_UV' undeclared (first use in this function)
XS.xs:1015: (Each undeclared identifier is reported only once
XS.xs:1015: for each function it appears in.)
XS.xs:1016: `IS_NUMBER_NEG' undeclared (first use in this function)
XS.xs: In function `decode_hv':
XS.xs:1128: warning: comparison is always false due to limited range of data type
XS.xs: In function `decode_json':
XS.xs:1397: `UNI_DISPLAY_QQ' undeclared (first use in this function)
make: *** [XS.o] Error 1