[flang][runtime] Initial support for offload build of FortranDecimal.

Author: vzakhari

flang/lib/Decimal/CMakeLists.txt

@@ -49,11 +49,17 @@ endif()
 # avoid an unwanted dependency on libstdc++.so.
 add_definitions(-U_GLIBCXX_ASSERTIONS)
 
-add_flang_library(FortranDecimal INSTALL_WITH_TOOLCHAIN
+set(sources
   binary-to-decimal.cpp
   decimal-to-binary.cpp
 )
 
+include(AddFlangOffloadRuntime)
+enable_cuda_compilation("${sources}")
+enable_omp_offload_compilation("${sources}")
+
+add_flang_library(FortranDecimal INSTALL_WITH_TOOLCHAIN ${sources})
+
 if (DEFINED MSVC)
   set(CMAKE_MSVC_RUNTIME_LIBRARY MultiThreaded)
   add_flang_library(FortranDecimal.static INSTALL_WITH_TOOLCHAIN
@@ -77,4 +83,4 @@ if (DEFINED MSVC)
   )
   add_dependencies(FortranDecimal FortranDecimal.static FortranDecimal.dynamic
     FortranDecimal.static_dbg FortranDecimal.dynamic_dbg)
-endif()
+endif()

flang/lib/Decimal/big-radix-floating-point.h

@@ -30,6 +30,10 @@
 #include <limits>
 #include <type_traits>
 
+// Some environments, viz. glibc 2.17, allow the macro HUGE
+// to leak out of <math.h>.
+#undef HUGE
+
 namespace Fortran::decimal {
 
 static constexpr std::uint64_t TenToThe(int power) {