Regularize use of PRIVATE_CXX.

Change-Id: Ifc628c67b5fa142cec59187f89f2d39df81160b9
diff --git a/core/combo/HOST_darwin-x86.mk b/core/combo/HOST_darwin-x86.mk
index a136041..855317f 100644
--- a/core/combo/HOST_darwin-x86.mk
+++ b/core/combo/HOST_darwin-x86.mk
@@ -59,7 +59,7 @@
 HOST_CUSTOM_LD_COMMAND := true
 
 define transform-host-o-to-shared-lib-inner
-    $(HOST_CXX) \
+    $(PRIVATE_CXX) \
         -dynamiclib -single_module -read_only_relocs suppress \
         $(HOST_GLOBAL_LD_DIRS) \
         $(HOST_GLOBAL_LDFLAGS) \
@@ -74,7 +74,7 @@
 endef
 
 define transform-host-o-to-executable-inner
-$(HOST_CXX) \
+$(PRIVATE_CXX) \
         -o $@ \
         -Wl,-dynamic -headerpad_max_install_names \
         $(HOST_GLOBAL_LD_DIRS) \
diff --git a/core/combo/TARGET_linux-arm.mk b/core/combo/TARGET_linux-arm.mk
index 506de1b..ebb6590 100644
--- a/core/combo/TARGET_linux-arm.mk
+++ b/core/combo/TARGET_linux-arm.mk
@@ -231,7 +231,7 @@
 endif
 
 define transform-o-to-shared-lib-inner
-$(TARGET_CXX) \
+$(PRIVATE_CXX) \
 	-nostdlib -Wl,-soname,$(notdir $@) -Wl,-T,$(BUILD_SYSTEM)/armelf.xsc \
 	-Wl,--gc-sections \
 	-Wl,-shared,-Bsymbolic \
@@ -252,7 +252,7 @@
 endef
 
 define transform-o-to-executable-inner
-$(TARGET_CXX) -nostdlib -Bdynamic -Wl,-T,$(BUILD_SYSTEM)/armelf.x \
+$(PRIVATE_CXX) -nostdlib -Bdynamic -Wl,-T,$(BUILD_SYSTEM)/armelf.x \
 	-Wl,-dynamic-linker,/system/bin/linker \
     -Wl,--gc-sections \
 	-Wl,-z,nocopyreloc \
@@ -271,7 +271,7 @@
 endef
 
 define transform-o-to-static-executable-inner
-$(TARGET_CXX) -nostdlib -Bstatic -Wl,-T,$(BUILD_SYSTEM)/armelf.x \
+$(PRIVATE_CXX) -nostdlib -Bstatic -Wl,-T,$(BUILD_SYSTEM)/armelf.x \
     -Wl,--gc-sections \
 	-o $@ \
 	$(TARGET_GLOBAL_LD_DIRS) \
diff --git a/core/combo/TARGET_linux-sh.mk b/core/combo/TARGET_linux-sh.mk
index 432191a..0cc72ec 100644
--- a/core/combo/TARGET_linux-sh.mk
+++ b/core/combo/TARGET_linux-sh.mk
@@ -114,7 +114,7 @@
 
 TARGET_CUSTOM_LD_COMMAND := true
 define transform-o-to-shared-lib-inner
-$(TARGET_CXX) \
+$(PRIVATE_CXX) \
 	-nostdlib -Wl,-soname,$(notdir $@) -Wl,-T,$(BUILD_SYSTEM)/shlelf.xsc \
 	-Wl,--gc-sections -Wl,-z,norelro \
 	-Wl,-shared,-Bsymbolic \
@@ -134,7 +134,7 @@
 endef
 
 define transform-o-to-executable-inner
-$(TARGET_CXX) -nostdlib -Bdynamic  -Wl,-T,$(BUILD_SYSTEM)/shlelf.x \
+$(PRIVATE_CXX) -nostdlib -Bdynamic  -Wl,-T,$(BUILD_SYSTEM)/shlelf.x \
 	-Wl,-dynamic-linker,/system/bin/linker \
 	-Wl,--gc-sections -Wl,-z,norelro \
 	-Wl,-z,nocopyreloc \
@@ -152,7 +152,7 @@
 endef
 
 define transform-o-to-static-executable-inner
-$(TARGET_CXX) -nostdlib -Bstatic  -Wl,-T,$(BUILD_SYSTEM)/shlelf.x \
+$(PRIVATE_CXX) -nostdlib -Bstatic  -Wl,-T,$(BUILD_SYSTEM)/shlelf.x \
 	-Wl,--gc-sections -Wl,-z,norelro \
 	-o $@ \
 	$(TARGET_GLOBAL_LD_DIRS) \
diff --git a/core/combo/TARGET_linux-x86.mk b/core/combo/TARGET_linux-x86.mk
index 3b05819..70a8ba6 100644
--- a/core/combo/TARGET_linux-x86.mk
+++ b/core/combo/TARGET_linux-x86.mk
@@ -117,7 +117,7 @@
 
 TARGET_CUSTOM_LD_COMMAND := true
 define transform-o-to-shared-lib-inner
-$(TARGET_CXX) \
+$(PRIVATE_CXX) \
 	$(PRIVATE_TARGET_GLOBAL_LDFLAGS) \
 	 -nostdlib -Wl,-soname,$(notdir $@) \
 	 -shared -Bsymbolic \
@@ -138,7 +138,7 @@
 
 
 define transform-o-to-executable-inner
-$(TARGET_CXX) \
+$(PRIVATE_CXX) \
 	$(TARGET_GLOBAL_LDFLAGS) \
 	-nostdlib -Bdynamic \
 	-Wl,-dynamic-linker,/system/bin/linker \
@@ -156,7 +156,7 @@
 endef
 
 define transform-o-to-static-executable-inner
-$(TARGET_CXX) \
+$(PRIVATE_CXX) \
 	$(TARGET_GLOBAL_LDFLAGS) \
 	-nostdlib -Bstatic \
 	-o $@ \