Add a build system for the C++ library and fix missing standard library
includes.  Upstream does not provide a build system for its C++
implementation.

diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..325bf0b
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,23 @@
+CXXFLAGS += -std=c++17 -fPIC
+CPPFLAGS += -I. $(shell pkg-config --cflags absl_flat_hash_map absl_strings gmock_main)
+ABSL_LIBS = $(shell pkg-config --libs absl_flat_hash_map absl_strings)
+TEST_LIBS = $(shell pkg-config --libs gmock_main)
+SOURCES = $(filter-out %_test.cc,$(wildcard cpp/*/*.cc))
+OBJECTS = $(SOURCES:.cc=.o)
+TEST_OBJECTS = $(patsubst %.cc,%.o,$(wildcard cpp/*/*_test.cc))
+LIBRARY = libmaterial-color-utilities.so
+
+all: $(LIBRARY)
+
+$(LIBRARY): $(OBJECTS)
+	$(CXX) -shared $(LDFLAGS) -Wl,-soname,$@ -o $@ $^ $(ABSL_LIBS)
+
+material-color-utilities-tests: $(TEST_OBJECTS) $(LIBRARY)
+	$(CXX) $(LDFLAGS) -o $@ $(TEST_OBJECTS) -L. -lmaterial-color-utilities $(TEST_LIBS)
+
+check: material-color-utilities-tests
+	LD_LIBRARY_PATH=. ./material-color-utilities-tests
+
+install: $(LIBRARY)
+	install -Dm755 $(LIBRARY) $(PREFIX)/lib/$(LIBRARY)
+	find cpp -name '*.h' -exec install -Dm644 {} $(PREFIX)/include/{} \;
diff --git a/cpp/temperature/temperature_cache.cc b/cpp/temperature/temperature_cache.cc
index 4fec3a2..8af11e6 100644
--- a/cpp/temperature/temperature_cache.cc
+++ b/cpp/temperature/temperature_cache.cc
@@ -17,6 +17,7 @@
 #include "cpp/temperature/temperature_cache.h"
 
 #include <algorithm>
+#include <cmath>
 #include <map>
 #include <vector>
 
@@ -60,7 +61,7 @@ Hct TemperatureCache::GetComplement() {
     Hct possible_answer = GetHctsByHue().at((int)round(hue));
     double relative_temp =
         (GetTempsByHct().at(possible_answer) - coldest_temp) / range;
-    double error = abs(complement_relative_temp - relative_temp);
+    double error = std::abs(complement_relative_temp - relative_temp);
     if (error < smallest_error) {
       smallest_error = error;
       answer = possible_answer;
@@ -89,7 +90,7 @@ std::vector<Hct> TemperatureCache::GetAnalogousColors(int count,
     int hue = SanitizeDegreesInt(start_hue + i);
     Hct hct = GetHctsByHue().at(hue);
     double temp = GetRelativeTemperature(hct);
-    double temp_delta = abs(temp - last_temp);
+    double temp_delta = std::abs(temp - last_temp);
     last_temp = temp;
     absolute_total_temp_delta += temp_delta;
   }
@@ -102,7 +103,7 @@ std::vector<Hct> TemperatureCache::GetAnalogousColors(int count,
     int hue = SanitizeDegreesInt(start_hue + hue_addend);
     Hct hct = GetHctsByHue().at(hue);
     double temp = GetRelativeTemperature(hct);
-    double temp_delta = abs(temp - last_temp);
+    double temp_delta = std::abs(temp - last_temp);
     total_temp_delta += temp_delta;
 
     double desired_total_temp_delta_for_index = (all_colors.size() * temp_step);
diff --git a/cpp/temperature/temperature_cache.h b/cpp/temperature/temperature_cache.h
index 17e7c17..492f6e5 100644
--- a/cpp/temperature/temperature_cache.h
+++ b/cpp/temperature/temperature_cache.h
@@ -18,6 +18,7 @@
 #define CPP_TEMPERATURE_TEMPERATURE_CACHE_H_
 
 #include <map>
+#include <optional>
 #include <vector>
 
 #include "cpp/cam/hct.h"