It looks like the build system is special-cased for clang on windows (using SLEEF_CLANG_ON_WINDOWS variable).
Most of these cases make sense, but in Configure.cmake we do not able GNUABI if SLEEF_CLANG_ON_WINDOWS and nothing seems to justify/explain it.
if (COMPILER_SUPPORTS_WEAK_ALIASES AND
NOT CMAKE_SYSTEM_PROCESSOR MATCHES "arm" AND
NOT CMAKE_SYSTEM_PROCESSOR MATCHES "^(powerpc|ppc)64" AND
NOT (SLEEF_CLANG_ON_WINDOWS) AND
NOT MINGW AND SLEEF_BUILD_GNUABI_LIBS)
set(ENABLE_GNUABI ${COMPILER_SUPPORTS_WEAK_ALIASES})
What is wrong with Clang on Windows and GNU ABI?
Remember at the time windows also implied x86, but soon it won't.
It looks like the build system is special-cased for clang on windows (using SLEEF_CLANG_ON_WINDOWS variable). Most of these cases make sense, but in Configure.cmake we do not able GNUABI if SLEEF_CLANG_ON_WINDOWS and nothing seems to justify/explain it.
What is wrong with Clang on Windows and GNU ABI?
Remember at the time windows also implied x86, but soon it won't.