From 73b774f5ebee56185b03f98bee81e0dd62fab9db Mon Sep 17 00:00:00 2001
From: Dmitrii Kuvaiskii <dmitrii.kuvaiskii@intel.com>
Date: Thu, 1 Oct 2020 00:24:34 -0700
Subject: [PATCH] [LibOS] Makefile: Revert commit 'Make sure to build GCC with
 GCC'

Unfortunately, specifying environment variables like CC, CXX, AS
during GCC build leads to strange errors. The official GCC docs
simply state "defining certain environment variables such as CC
can interfere with the functioning of make". So we unset them
explicitly for the GCC build.
---
 LibOS/Makefile | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/LibOS/Makefile b/LibOS/Makefile
index 2f53123f..9dd2efad 100644
--- a/LibOS/Makefile
+++ b/LibOS/Makefile
@@ -125,7 +125,10 @@ $(GLIBC_SRC)/dlfcn/Versions: $(GLIBC_SRC)/.configured
 # makes sense only on x86_64 platforms. NOTE: We'd prefer to build libgomp.so.1 alone but it is
 # impossible (the only way to build it is as part of the complete GCC build).
 #
-# Override CC, CXX, AS in case we're compiling the rest of the project with clang.
+# We explicitly unset CC, CXX, AS environment variables for the case we're compiling the rest of the
+# project with clang. This is because in GCC build, "defining certain environment variables such as
+# CC can interfere with the functioning of make" (https://gcc.gnu.org/install/build.html). Indeed,
+# defining CC=gcc or CC=clang leads to errors during GCC build.
 # ------------------------------------------------------------------------------------------------
 GCC_VERSION ?= 10.2.0
 GCC_SRC = gcc-$(GCC_VERSION)
@@ -139,14 +142,14 @@ GCC_RUNTIME = $(addprefix $(RUNTIME_DIR)/, $(notdir $(GCC_TARGET)))
 
 $(GCC_BUILD_DIR)/Build.success: $(GCC_BUILD_DIR)/Makefile
 	@echo "Building gcc, may take a while to finish. Warning messages may show up. If this process terminates with failures, see \"$(GCC_BUILD_DIR)/gcc-build.log\" for more information."
-	(CC=gcc CXX=g++ AS=gcc $(MAKE) -C $(GCC_BUILD_DIR) 2>&1 > gcc-build.log) && touch $@
+	(unset CC CXX AS; $(MAKE) -C $(GCC_BUILD_DIR) 2>&1 > gcc-build.log) && touch $@
 
 $(GCC_TARGET): $(GCC_BUILD_DIR)/Build.success
 
 $(GCC_BUILD_DIR)/Makefile: $(GCC_SRC)/.configured
 	mkdir -p $(GCC_BUILD_DIR)
 	(cd $(GCC_BUILD_DIR) || exit 1; \
-	CC=gcc CXX=g++ AS=gcc \
+	unset CC CXX AS; \
 	../$(GCC_SRC)/configure --prefix=$(RUNTIME_DIR) \
 		--enable-languages=c \
 		--disable-multilib \