build: make out-of-tree builds with Python bindings work on msys2

build: make out-of-tree builds with Python bindings work on msys2

When doing an out of tree build on msys2 with
`--enable-python-bindings`, where the path to configure is absolute, I
get:

    Making all in bindings/python/bt2
    make[3]: Entering directory '/home/smarchi/build/babeltrace-mingw-w64-ucrt-x86_64/src/bindings/python/bt2'
    touch copy-static-deps.stamp
      SWIG      bt2/native_bt.c
    CC="ccache gcc" CFLAGS="-IC:/msys64/ucrt64/include/glib-2.0 -IC:/msys64/ucrt64/lib/glib-2.0/include -fvisibility=hidden -pthread -IC:/msys64/ucrt64/include/glib-2.0 -IC:/msys64/ucrt64/lib/glib-2.0/include   -Wall -Wextra -Wmissing-prototypes -Wmissing-declarations -Wnull-derefere
nce -Wundef -Wredundant-decls -Wshadow -Wjump-misses-init -Wsuggest-attribute=format -Wnested-externs -Wwrite-strings -Wformat=2 -Wstrict-aliasing -Wmissing-noreturn -Winit-self -Wduplicated-cond -Wduplicated-branches -Wlogical-op -Wsuggest-override -Wno-sign-compare -Wno-cast-functi
on-type -Wno-maybe-uninitialized -Wold-style-definition -Wstrict-prototypes -g -O2 -Wno-shadow -Wno-null-dereference -Wno-deprecated-declarations -Wno-redundant-decls -Wno-missing-field-initializers -Wno-unused-parameter -Wno-undef" CPPFLAGS="-I/home/smarchi/src/babeltrace/include -I
../../../../src -I/home/smarchi/src/babeltrace/src -include common/config.h  -I/home/smarchi/src/babeltrace/src/bindings/python/bt2/bt2" LDFLAGS="-L../../../../src/lib/.libs  -lgmodule-2.0 -lglib-2.0 -lintl -LC:/msys64/ucrt64/lib -lpython3.11  -lversion -lshlwapi -lpathcch -lbcrypt -
lm   -lgmodule-2.0 -lglib-2.0 -lintl" /ucrt64/bin/python ./setup.py build --force
    [...]
    ccache gcc -IC:/msys64/ucrt64/include/glib-2.0 -IC:/msys64/ucrt64/lib/glib-2.0/include -fvisibility=hidden -pthread -IC:/msys64/ucrt64/include/glib-2.0 -IC:/msys64/ucrt64/lib/glib-2.0/include -Wall -Wextra -Wmissing-prototypes -Wmissing-declarations -Wnull-dereference -Wundef -Wr
edundant-decls -Wshadow -Wjump-misses-init -Wsuggest-attribute=format -Wnested-externs -Wwrite-strings -Wformat=2 -Wstrict-aliasing -Wmissing-noreturn -Winit-self -Wduplicated-cond -Wduplicated-branches -Wlogical-op -Wsuggest-override -Wno-sign-compare -Wno-cast-function-type -Wno-ma
ybe-uninitialized -Wold-style-definition -Wstrict-prototypes -g -O2 -Wno-shadow -Wno-null-dereference -Wno-deprecated-declarations -Wno-redundant-decls -Wno-missing-field-initializers -Wno-unused-parameter -Wno-undef -IC:/msys64/ucrt64/include/glib-2.0 -IC:/msys64/ucrt64/lib/glib-2.0
/include -fvisibility=hidden -pthread -IC:/msys64/ucrt64/include/glib-2.0 -IC:/msys64/ucrt64/lib/glib-2.0/include -Wall -Wextra -Wmissing-prototypes -Wmissing-declarations -Wnull-dereference -Wundef -Wredundant-decls -Wshadow -Wjump-misses-init -Wsuggest-attribute=format -Wnested-ext
erns -Wwrite-strings -Wformat=2 -Wstrict-aliasing -Wmissing-noreturn -Winit-self -Wduplicated-cond -Wduplicated-branches -Wlogical-op -Wsuggest-override -Wno-sign-compare -Wno-cast-function-type -Wno-maybe-uninitialized -Wold-style-definition -Wstrict-prototypes -g -O2 -Wno-shadow -W
no-null-dereference -Wno-deprecated-declarations -Wno-redundant-decls -Wno-missing-field-initializers -Wno-unused-parameter -Wno-undef -IC:/msys64/home/smarchi/src/babeltrace/include -I../../../../src -I/home/smarchi/src/babeltrace/src -include common/config.h -I/home/smarchi/src/bab
eltrace/src/bindings/python/bt2/bt2 -IC:/msys64/ucrt64/include/python3.11 -c /home/smarchi/src/babeltrace/src/bindings/python/bt2/bt2/logging.c -o build/temp.mingw_x86_64_ucrt-3.11/home/smarchi/src/babeltrace/src/bindings/python/bt2/bt2/logging.o
    cc1.exe: warning: command-line option '-Wsuggest-override' is valid for C++/ObjC++ but not for C
    cc1.exe: fatal error: /home/smarchi/src/babeltrace/src/bindings/python/bt2/bt2/logging.c: No such file or directory
    compilation terminated.
    error: command 'C:\\msys64\\ucrt64\\bin/ccache.exe' failed with exit code 1
    make[3]: *** [Makefile:735: build-python-bindings.stamp] Error 1
    make[3]: Leaving directory '/home/smarchi/build/babeltrace-mingw-w64-ucrt-x86_64/src/bindings/python/bt2'

For 'in-tree' builds all the paths are relative and thus compatible with
native windows binaries while in an 'out-of-tree' build some of the
paths are absolute and thus incompatible. The MSYS2 shell does a lot of
'magic' conversion [1] on paths passed as arguments and through environment
variables but the heuristics are limited and it doesn't apply when
binaries are called directly without using the shell.

The first issue is the include paths in the CFLAGS and CPPFLAGS
environment variables which don't get converted because they start with
'-I'.

The second issue is that the path to 'logging.c' in the generated
'setup.py is absolute:

    sources=["bt2/native_bt.c", "/home/smarchi/src/babeltrace/src/bindings/python/bt2/bt2/logging.c"],

When distutils invokes gcc to compile this file, it spawns it directly,
not through a shell, so no automatic Unix -> Windows path conversion
takes place.

Fix both of those issues by modifying 'setup.py' to detect the MSYS2
environment and convert absolute path to Windows style using the
'cygpath' command.

[1] https://www.msys2.org/docs/filesystem-paths/

Change-Id: I9003878a6582a0dc3f4ee18b07885f332348b8bf
Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Reviewed-on: https://review.lttng.org/c/babeltrace/+/12397
Tested-by: jenkins <jenkins@lttng.org>
Reviewed-by: Simon Marchi <simon.marchi@efficios.com>