libgomp.texi: For HIP interop, mention cpp defines to set

The HIP header files recognize the used compiler, defaulting to either AMD
or Nvidia/CUDA; thus, the alternative way of explicitly defining a macro is
less prominently documented. With GCC, the user has to define the
preprocessor macro manually. Hence, as a service to the user, mention
__HIP_PLATFORM_AMD__ and __HIP_PLATFORM_NVIDIA__ in the interop documentation,
even though it has only indirectly to do with GCC and its interop support.

Note to commit-log readers, only: For Fortran, the hipfort modules can be
used; when compiling the hipfort package (defaults to use gfortran), it
generates the module (*.mod) files in include/hipfort/{amdgcn,nvidia}/ such
that the choice is made by setting the respective include path.

libgomp/ChangeLog:

	* libgomp.texi (gcn interop, nvptx interop): For HIP with C/C++, add
	a note about setting a preprocessor define.

1 files changed, 6 insertions, 0 deletions

diff --git a/libgomp/libgomp.texi b/libgomp/libgomp.texi
index dfd189b..6909c2b 100644
--- a/libgomp/libgomp.texi
+++ b/libgomp/libgomp.texi
@@ -6945,6 +6945,9 @@ or string (str) data type, call @code{omp_get_interop_int},
 Note that @code{device_num} is the OpenMP device number
 while @code{device} is the HIP device number or HSA device handle.
 
+When using HIP with C and C++, the @code{__HIP_PLATFORM_AMD__} preprocessor
+macro must be defined before including the HIP header files.
+
 For the API routine call, add the prefix @code{omp_ipr_} to the property name;
 for instance:
 @smallexample
@@ -7107,6 +7110,9 @@ or string (str) data type, call @code{omp_get_interop_int},
 Note that @code{device_num} is the OpenMP device number while @code{device}
 is the CUDA, CUDA Driver, or HIP device number.
 
+When using HIP with C and C++, the @code{__HIP_PLATFORM_NVIDIA__} preprocessor
+macro must be defined before including the HIP header files.
+
 For the API routine call, add the prefix @code{omp_ipr_} to the property name;
 for instance:
 @smallexample