Cross-compiling for Raspberry Pi I fails using Linaro 7.4.1 toolchain

Question

I downloaded the latest Linaro toolchain (https://releases.linaro.org/components/toolchain/binaries/latest-7/arm-linux-gnueabihf/) to cross-compile C++ code for different Raspberry Pis which running a Raspbian Buster. For testing I used a simple hello world code. If I compile this using

<path to toolchain>/arm-linux-gnueabihf-g++ main.cpp -o helloworld

the programme runs fine on Raspberry Pi II as well as on Raspberry Pi III models but on Raspberry Pi I it throws a

Segmentation fault

For some other code (Qt) the execution fails with

Illegal instruction

If I compile the same code directly on the Raspberry Pi I, it works fine.

So far I understood is this due to that the toolchain compiles for arm7 by default. I tried to force arm6 compatibility using

<path to toolchain>/arm-linux-gnueabihf-g++ main.cpp -o helloworld -marm

But this makes no difference. Further I tried

<path to toolchain>/arm-linux-gnueabihf-g++ main.cpp -o helloworld march=armv6z -mtune=arm1176jzf-s -mfpu=vfp -mfloat-abi=hard

however, this results in compiler errors:

In file included from /home/development/linaro/gcc-linaro-7.4.1-2019.02-i686_arm-linux-gnueabihf/arm-linux-gnueabihf/include/c++/7.4.1/exception:38:0,
                 from /home/development/linaro/gcc-linaro-7.4.1-2019.02-i686_arm-linux-gnueabihf/arm-linux-gnueabihf/include/c++/7.4.1/ios:39,
                 from /home/development/linaro/gcc-linaro-7.4.1-2019.02-i686_arm-linux-gnueabihf/arm-linux-gnueabihf/include/c++/7.4.1/ostream:38,
                 from /home/development/linaro/gcc-linaro-7.4.1-2019.02-i686_arm-linux-gnueabihf/arm-linux-gnueabihf/include/c++/7.4.1/iostream:39,
                 from main.cpp:2:
/home/development/linaro/gcc-linaro-7.4.1-2019.02-i686_arm-linux-gnueabihf/arm-linux-gnueabihf/include/c++/7.4.1/bits/exception.h: In Konstruktor »std::exception::exception()«:
/home/development/linaro/gcc-linaro-7.4.1-2019.02-i686_arm-linux-gnueabihf/arm-linux-gnueabihf/include/c++/7.4.1/bits/exception.h:63:39: nicht implementiert: Thumb-1 Hardware-Gleitkomma VFP ABI
     exception() _GLIBCXX_USE_NOEXCEPT { }

where "nicht implementiert: Thumb-1 Hardware-Gleitkomma" means "not implemented: Thumb-1 Hardware floating point".

Does anybody has an idea, how to use the toolchain to compile for armv6, i.e. Raspberry Pi I?