linking errors on powerpc/kfreebsd Debians

As reported by Thibaut Paumard, GDL fails to link on powerpc and kfreebsd Debians due to the following error:

gdl-overload.o: In function std::string::_M_data() const': /«PKGBUILDDIR»/src/overload.cpp:94: multiple definition of_GDL_OBJECT_OverloadIsTrue(EnvUDT)'
gdl-overload.o:/«PKGBUILDDIR»/src/overload.cpp:94: first defined here
gdl-overload.o: In function OverloadOperatorIndexFun(std::string)': /«PKGBUILDDIR»/src/overload.cpp:66: multiple definition ofOverloadOperatorIndexFun(std::string)'
gdl-overload.o:/«PKGBUILDDIR»/src/overload.cpp:66: first defined here
gdl-overload.o: In function std::string::_M_data() const': /usr/include/c++/4.8/bits/basic_string.h:293: multiple definition ofOverloadOperatorIndexPro(std::string)'
gdl-overload.o:/usr/include/c++/4.8/bits/basic_string.h:293: first
defined here
gdl-overload.o: In function ThrowFromInternalUDSub(EnvUDT*, std::string const&)': /«PKGBUILDDIR»/src/overload.cpp:84: multiple definition ofThrowFromInternalUDSub(EnvUDT, std::string const&)'
gdl-overload.o:/«PKGBUILDDIR»/src/overload.cpp:84: first defined here
gdl-overload.o: In function _GDL_OBJECT_OverloadBracketsLeftSide(EnvUDT*)': /«PKGBUILDDIR»/src/overload.cpp:103: multiple definition of_GDL_OBJECT_OverloadBracketsLeftSide(EnvUDT)'
gdl-overload.o:/«PKGBUILDDIR»/src/overload.cpp:103: first defined here
gdl-overload.o: In function _GDL_OBJECT_OverloadEQOp(EnvUDT*)': /«PKGBUILDDIR»/src/overload.cpp:240: multiple definition of_GDL_OBJECT_OverloadEQOp(EnvUDT)'
gdl-overload.o:/«PKGBUILDDIR»/src/overload.cpp:240: first defined here
gdl-overload.o: In function _GDL_OBJECT_OverloadNEOp(EnvUDT*)': /«PKGBUILDDIR»/src/overload.cpp:328: multiple definition of_GDL_OBJECT_OverloadNEOp(EnvUDT)'
gdl-overload.o:/«PKGBUILDDIR»/src/overload.cpp:328: first defined here
gdl-overload.o: In function
_GDL_OBJECT_OverloadReportIllegalOperation(EnvUDT*)': /«PKGBUILDDIR»/src/overload.cpp:419: multiple definition of_GDL_OBJECT_OverloadReportIllegalOperation(EnvUDT)'
gdl-overload.o:/«PKGBUILDDIR»/src/overload.cpp:419: first defined here
gdl-overload.o: In function SetupOverloadSubroutines()': /«PKGBUILDDIR»/src/overload.cpp:426: multiple definition ofSetupOverloadSubroutines()'
gdl-overload.o:/«PKGBUILDDIR»/src/overload.cpp:426: first defined here
gdl-overload.o: In function
_GDL_OBJECT_OverloadBracketsRightSide(EnvUDT*)': /«PKGBUILDDIR»/src/overload.cpp:139: multiple definition of_GDL_OBJECT_OverloadBracketsRightSide(EnvUDT*)'
gdl-overload.o:/«PKGBUILDDIR»/src/overload.cpp:139: first defined here
gdl-overload.o: In function std::string::_M_data() const': /«PKGBUILDDIR»/src/overload.cpp:94: multiple definition ofoverloadOperatorNames'
gdl-overload.o:/«PKGBUILDDIR»/src/overload.cpp:94: first defined here
collect2: error: ld returned 1 exit status