Regression: #677 reopens #632

[christoph-conrads]

Description

Issue #632 ensured the availability of lapack.h when LAPACKE support was disabled: lapack.h includes lapacke_mangling.h, before #632 LAPACKE support had to be enabled to have lapacke_mangling.h generated, and the fix for this issue was to generate lapacke_mangling.h unconditionally, see #637 for the corresponding pull request. PR #677 (its commit 8d3ae00 to be precise) disables this code again.

Example:

$ git clone --depth=1 -- 'https://github.com/reference-lapack/lapack.git'
Cloning into 'lapack'...
remote: Enumerating objects: 6554, done.
remote: Counting objects: 100% (6554/6554), done.
remote: Compressing objects: 100% (5504/5504), done.
remote: Total 6554 (delta 5693), reused 1118 (delta 1048), pack-reused 0
Receiving objects: 100% (6554/6554), 5.24 MiB | 7.03 MiB/s, done.
Resolving deltas: 100% (5693/5693), done.
$ mkdir build 
$ cd build
$ cmake ../lapack/
-- The Fortran compiler identification is GNU 11.2.0
-- The C compiler identification is GNU 11.2.0
[...]
-- Build files have been written to: /tmp/build
$ ls # note no include directory
BLAS                     INSTALL                      lapack-config.cmake
CMakeCache.txt           LAPACKE                      lapack-targets.cmake
CMakeFiles               Makefile                     lapack.pc
CPackConfig.cmake        SRC                          lib
CPackSourceConfig.cmake  cmake_install.cmake
CTestCustom.cmake        lapack-config-version.cmake
$ cmake -DLAPACKE=ON .
[...]
-- Using supplied NETLIB BLAS implementation
-- Using supplied NETLIB LAPACK implementation
-- Detecting Fortran/C Interface
-- Detecting Fortran/C Interface - Found GLOBAL and MODULE mangling
-- Verifying Fortran/C Compiler Compatibility
-- Verifying Fortran/C Compiler Compatibility - Success
-- LAPACKE enabled
-- Build LAPACKE single precision real: ON
-- Build LAPACKE double precision real: ON
-- Build LAPACKE single precision complex: ON
-- Build LAPACKE double precision complex: ON
[...]
-- Build files have been written to: /tmp/build
$ ls include/
lapack.h  lapacke.h  lapacke_config.h  lapacke_mangling.h  lapacke_utils.h

Checklist

• I've included a minimal example to reproduce the issue
• I'd be willing to make a PR to solve this issue

I would like to fix this but I do not have access to XLF compilers.

[christoph-conrads]

Thank you @friedc and @weslleyspereira for looking into this.