Disable Pigweed atomics on riscv_tinysis

This is not supported by this platform.

Bug: N/A
Flag: EXEMPT build only
Test: Presubmits
Change-Id: I2c9da797c40673e9463bbd5c092e9a731a474eec
diff --git a/build/variant/aosp_riscv_tinysys_common.mk b/build/variant/aosp_riscv_tinysys_common.mk
index 136f2a4..1950a1d 100644
--- a/build/variant/aosp_riscv_tinysys_common.mk
+++ b/build/variant/aosp_riscv_tinysys_common.mk
@@ -65,6 +65,11 @@
   TINYSYS_CFLAGS += -DCFG_STATIC_ALLOCATE
   TINYSYS_CFLAGS += -DconfigSUPPORT_STATIC_ALLOCATION=1
 
+  # Disable atomic operations in Pigweed as they are not supported on this platform.
+  # This will eventually be deprecated by the Pigweed team when they move to
+  # portable atomics with pw_atomic.
+  TINYSYS_CFLAGS += -DPW_ALLOCATOR_HAS_ATOMICS=0
+
   # Compiling flags ##############################################################
 
   TINYSYS_CFLAGS += $(FLATBUFFERS_CFLAGS)