gmp guile icu4c ncurses xmlrpc: use BUILD_CC/CXX portability variable

src/gmp.mk

@@ -20,7 +20,7 @@ define $(PKG)_UPDATE
 endef
 
 define $(PKG)_BUILD
-    cd '$(1)' && CC_FOR_BUILD=gcc ./configure \
+    cd '$(1)' && CC_FOR_BUILD=$(BUILD_CC) ./configure \
         $(MXE_CONFIGURE_OPTS) \
         --enable-cxx \
         --without-readline

src/guile.mk

@@ -23,7 +23,7 @@ define $(PKG)_BUILD
     # The setting "scm_cv_struct_timespec=no" ensures that Guile
     # won't try to use the "struct timespec" from <pthreads.h>,
     # which would fail because we tell Guile not to use Pthreads.
-    cd '$(1)' && CC_FOR_BUILD=gcc ./configure \
+    cd '$(1)' && CC_FOR_BUILD=$(BUILD_CC) ./configure \
         --host='$(TARGET)' \
         --build="`config.guess`" \
         --prefix='$(PREFIX)/$(TARGET)' \

src/icu4c.mk

@@ -22,7 +22,7 @@ endef
 define $(PKG)_BUILD_COMMON
     cd '$(1)/source' && autoreconf -fi
     mkdir '$(1).native' && cd '$(1).native' && '$(1)/source/configure' \
-        CC=gcc CXX=g++
+        CC=$(BUILD_CC) CXX=$(BUILD_CXX)
     $(MAKE) -C '$(1).native' -j '$(JOBS)'
 
     mkdir '$(1).cross' && cd '$(1).cross' && '$(1)/source/configure' \

src/ncurses.mk

@@ -35,8 +35,8 @@ define $(PKG)_BUILD
         --host='$(TARGET)' \
         --build="`config.guess`" \
         --prefix=$(PREFIX)/$(TARGET) \
-        --with-build-cc=gcc \
-        --with-build-cpp=cpp \
+        --with-build-cc=$(BUILD_CC) \
+        --with-build-cpp='$(BUILD_CC) -E' \
         --disable-home-terminfo \
         --enable-sp-funcs \
         --enable-term-driver \

src/xmlrpc-c.mk

@@ -20,8 +20,8 @@ define $(PKG)_UPDATE
 endef
 
 $(PKG)_MAKE_OPTS = \
-    BUILDTOOL_CC=gcc \
-    BUILDTOOL_CCLD=gcc \
+    BUILDTOOL_CC=$(BUILD_CC) \
+    BUILDTOOL_CCLD=$(BUILD_CC) \
     SHARED_LIB_TYPE=@xmlrpc-c-shared-lib-type@ \
     MUST_BUILD_SHLIB=@xmlrpc-c-must-build-shlib@