Fix FortranFloat128Math include path

Author: Meinersbur

flang-rt/README.md

@@ -100,10 +100,15 @@ cmake -S <path-to-llvm-project>/runtimes                         \
   -GNinja                                                        \
   -DLLVM_BINARY_DIR=<path-to-llvm-builddir>                      \
   -DCMAKE_Fortran_COMPILER=<path-to-llvm-builddir>/bin/flang-new \
+  -DCMAKE_Fortran_COMPILER_WORKS=yes                             \
   -DLLVM_ENABLE_RUNTIMES=flang-rt                                \
   ...
 ```
 
+The `CMAKE_Fortran_COMPILER_WORKS` parameter must be set because otherwise CMake
+will test whether the Fortran compiler can compile and link programs which will
+obviously fail without a runtime library available yet.
+
 Building flang-rt for cross-compilation triple, the target triple can
 be selected using `LLVM_DEFAULT_TARGET_TRIPLE` AND `LLVM_RUNTIMES_TARGET`.
 Of course, flang-rt can be built multiple times with different build

flang-rt/lib/FortranFloat128Math/CMakeLists.txt

@@ -98,13 +98,19 @@ if (FLANG_RUNTIME_F128_MATH_LIB)
     add_flangrt_library(FortranFloat128Math STATIC INSTALL_WITH_TOOLCHAIN
       ${sources})
    endif ()
+   target_include_directories(FortranFloat128Math PRIVATE
+     "${FLANGRT_SOURCE_DIR}/lib/flang_rt"
+     )
 elseif (HAVE_LDBL_MANT_DIG_113)
   # We can use 'long double' versions from libc.
   check_library_exists(m sinl "" FOUND_LIBM)
   if (FOUND_LIBM)
     target_compile_definitions(FortranFloat128MathILib INTERFACE
       HAS_LIBM
       )
+    target_include_directories(FortranFloat128MathILib INTERFACE
+      "${FLANGRT_SOURCE_DIR}/lib/flang_rt"
+      )
     target_sources(FortranFloat128MathILib INTERFACE ${sources})
   else()
     message(FATAL_ERROR "flang-rt cannot build without libm")
@@ -116,6 +122,9 @@ else()
     target_compile_definitions(FortranFloat128MathILib INTERFACE
       HAS_LIBMF128
       )
+    target_include_directories(FortranFloat128MathILib INTERFACE
+      "${FLANGRT_SOURCE_DIR}/lib/flang_rt"
+      )
     # Enable this, when math-entries.h and complex-math.h is ready.
     # target_sources(FortranFloat128MathILib INTERFACE ${sources})
   endif()