QNX: Compiler and feature detection fixes
Tested compiler detection with the QNX 7.0 list of compiler targets:
- gcc_ntoaarch64le
- gcc_ntoaarch64le_cxx
- gcc_ntoarmv7le
- gcc_ntoarmv7le_cxx
- gcc_ntox86_cxx
- gcc_ntoaarch64le_gpp
- gcc_ntox86_64_gpp
- gcc_ntoarmv7le_gpp
- gcc_ntox86_64_cxx
- gcc_ntox86
- gcc_ntox86_gpp
- gcc_ntox86_64
This commit fixes some of the problems described in: https://cristianadam.eu/20181202/a-better-qnx-cmake-toolchain-file/