Makefile: set CGO_LDFLAGS=-latomic on arm/v6

Compiling with Go >= 1.22 on arm/v6 is failing with the following error
message:

27.84 gcc_libinit.c:44:8: error: large atomic operation may incur significant performance penalty; the access size (4 bytes) exceeds the max lock-free size (0  bytes) [-Werror,-Watomic-alignment]

For these Go versions, we need to manually link to libatomic as arm/v6
does not support atomic intrinsics and neither the CGo, nor the C
toolchain automatically link to that library.

Signed-off-by: Albin Kerouanton <[email protected]>

Author: akerouanton

Makefile

@@ -15,6 +15,17 @@ ifeq "$(shell go env GOOS)" "darwin"
 	export CGO_CFLAGS = -mmacosx-version-min=$(MACOSX_DEPLOYMENT_TARGET)
 endif
 
+ifeq "$(shell go env GOOS)/$(shell go env GOARCH)/$(shell go env GOARM)" "linux/arm/6"
+	# Neither the CGo compiler, nor the C toolchain automatically link to
+	# libatomic when the architecture doesn't support atomic intrinsics, as is
+	# the case for arm/v6.
+	#
+	# Here's the error we get when this is not done (see https://github.com/docker/docker-credential-helpers/pull/340#issuecomment-2437593837):
+	#
+	# gcc_libinit.c:44:8: error: large atomic operation may incur significant performance penalty; the access size (4 bytes) exceeds the max lock-free size (0  bytes) [-Werror,-Watomic-alignment]
+	export CGO_LDFLAGS=-latomic
+endif
+
 .PHONY: all
 all: cross