Allow overriding build type via env vars

Author: achirkin

build.sh

@@ -82,7 +82,7 @@ VERBOSE_FLAG=""
 BUILD_TESTS=ON
 BUILD_MG_ALGOS=ON
 BUILD_MNMG_TESTS=OFF
-BUILD_TYPE=Release
+BUILD_TYPE=${LIBCUVS_BUILD_TYPE:=Release}
 COMPILE_LIBRARY=OFF
 INSTALL_TARGET=install
 BUILD_REPORT_METRICS=""