makefile:use local gcc when native compiling

[ningmingxiao]

fix

cgo: C compiler "x86_64-linux-gnu-gcc" not found: exec: "x86_64-linux-gnu-gcc": executable file not found in $PATH

[afbjorklund]

The idea is OK, but it should not need an extra variable to be set...

Maybe check go env GOOS (without GOOS set) versus $GOOS?

[ningmingxiao]

can you describe clearly ? thanks @afbjorklund

[afbjorklund]

We should be able to detect when doing a cross-compile, without requiring that information from the user?

The main issue is that the format of uname -s and GOOS is slightly different (as with uname -m and GOARCH)

Most Linux distributions feature both, so it has not been a problem.

i.e. both gcc and x86_64-linux-gnu-gcc

[afbjorklund]

Ah, we already have some handy variables to use:

# returns difference between GOOS GOARCH and GOHOSTOS GOHOSTARCH.
cross_compiling = $(call diff,$(GOOS) $(GOARCH),$(GOHOSTOS) $(GOHOSTARCH))
# returns true if cross_compiling is empty.
native_compiling = $(if $(cross_compiling),,true)

We don't need to set anything, for a native build.

i.e. there is no need to hardcode gcc, but let go

[ningmingxiao]

how about

CC = $(call to_uname_m,$(GOARCH))-linux-gnu-gcc
ifeq ($(native_compiling),true)
	CC = gcc
endif

my host doesn't have x86_64-linux-gnu-gcc
and some os have
x86_64-anolis-linux-gcc instead of x86_64-linux-gnu-gcc

[afbjorklund]

If your host needs something special, you can override CC

make GOOS=linux GOARCH=... CC=my-gcc

But you can simplify it to:

ifeq ($(cross_compiling),true)
# CC is required for cross-compiling on Linux.
CC = $(call to_uname_m,$(GOARCH))-linux-gnu-gcc
endif

Might need to move the declarations in the file, though.

EDIT: typo

[ningmingxiao]

done, thank you.

[afbjorklund]

Tests are failing, so the new test is not working properly. (or the comment is wrong, and it always need CC?)

[afbjorklund]

The cross_compiling variable is empty when false (and the diff, when true), unlike native_compiling <sigh>

+ifneq ($(cross_compiling),)
 # CC is required for cross-compiling on Linux.
 CC = $(call to_uname_m,$(GOARCH))-linux-gnu-gcc
+endif