Fix up targets.json to replace instances of default_lib that have crept

across from master during automatic merging, with default_build (which is
the correct form for 5.1)

Author: adbridge

hal/targets.json

@@ -616,7 +616,7 @@
         "progen": {"target": "nucleo-f030r8"},
         "detect_code": ["0725"],
         "device_has": ["ANALOGIN", "I2C", "I2CSLAVE", "INTERRUPTIN", "PORTIN", "PORTINOUT", "PORTOUT", "PWMOUT", "RTC", "SERIAL", "SLEEP", "SPI", "SPISLAVE", "STDIO_MESSAGES"],
-        "default_lib": "small",
+        "default_build": "small",
         "release_versions": ["2"]
     },
     "NUCLEO_F031K6": {
@@ -718,7 +718,7 @@
         "progen": {"target": "nucleo-f302r8"},
         "detect_code": ["0705"],
         "device_has": ["ANALOGIN", "ANALOGOUT", "CAN", "I2C", "I2CSLAVE", "INTERRUPTIN", "LOWPOWERTIMER", "PORTIN", "PORTINOUT", "PORTOUT", "PWMOUT", "RTC", "SERIAL", "SERIAL_ASYNCH", "SERIAL_FC", "SLEEP", "SPI", "SPISLAVE", "STDIO_MESSAGES"],
-        "default_lib": "small",
+        "default_build": "small",
         "release_versions": ["2"]
     },
     "NUCLEO_F303K8": {
@@ -731,7 +731,7 @@
         "inherits": ["Target"],
         "progen": {"target": "nucleo-f303k8"},
         "detect_code": ["0775"],
-        "default_lib": "small",
+        "default_build": "small",
         "device_has": ["ANALOGIN", "ANALOGOUT", "CAN", "I2C", "I2CSLAVE", "INTERRUPTIN", "LOWPOWERTIMER", "PORTIN", "PORTINOUT", "PORTOUT", "PWMOUT", "RTC", "SERIAL", "SERIAL_FC", "SLEEP", "SPI", "SPISLAVE", "STDIO_MESSAGES"],
         "release_versions": ["2"]
     },
@@ -769,7 +769,7 @@
         "progen": {"target": "nucleo-f334r8"},
         "detect_code": ["0735"],
         "device_has": ["ANALOGIN", "ANALOGOUT", "CAN", "I2C", "I2CSLAVE", "INTERRUPTIN", "LOWPOWERTIMER", "PORTIN", "PORTINOUT", "PORTOUT", "PWMOUT", "RTC", "SERIAL", "SERIAL_ASYNCH", "SERIAL_FC", "SLEEP", "SPI", "SPISLAVE", "STDIO_MESSAGES"],
-        "default_lib": "small",
+        "default_build": "small",
         "release_versions": ["2"]
     },
     "NUCLEO_F401RE": {
@@ -946,7 +946,7 @@
         "progen": {"target": "nucleo-l053r8"},
         "detect_code": ["0715"],
         "device_has": ["ANALOGIN", "ANALOGOUT", "I2C", "I2CSLAVE", "INTERRUPTIN", "LOWPOWERTIMER", "PORTIN", "PORTINOUT", "PORTOUT", "PWMOUT", "RTC", "SERIAL", "SERIAL_FC", "SERIAL_ASYNCH", "SLEEP", "SPI", "SPISLAVE", "STDIO_MESSAGES"],
-        "default_lib": "small",
+        "default_build": "small",
         "release_versions": ["2"]
     },
     "NUCLEO_L073RZ": {
@@ -1057,7 +1057,7 @@
         "progen": {"target": "disco-f334c8"},
         "detect_code": ["0810"],
         "device_has": ["ANALOGIN", "ANALOGOUT", "I2C", "I2CSLAVE", "INTERRUPTIN", "LOWPOWERTIMER", "PORTIN", "PORTINOUT", "PORTOUT", "PWMOUT", "RTC", "RTC_LSI", "SERIAL", "SERIAL_ASYNCH", "SERIAL_FC", "SLEEP", "SPI", "SPISLAVE", "STDIO_MESSAGES"],
-        "default_lib": "small",
+        "default_build": "small",
         "release_versions": ["2"]
     },
     "DISCO_F407VG": {
@@ -1101,7 +1101,7 @@
         "supported_toolchains": ["ARM", "uARM", "IAR", "GCC_ARM"],
         "progen": {"target": "disco-l053c8"},
         "device_has": ["ANALOGIN", "ANALOGOUT", "I2C", "I2CSLAVE", "INTERRUPTIN", "LOWPOWERTIMER", "PORTIN", "PORTINOUT", "PORTOUT", "PWMOUT", "RTC", "SERIAL", "SERIAL_FC", "SLEEP", "SPI", "SPISLAVE", "STDIO_MESSAGES"],
-        "default_lib": "small",
+        "default_build": "small",
         "release_versions": ["2"]
     },
     "DISCO_F746NG": {
@@ -1187,7 +1187,7 @@
         "supported_toolchains": ["ARM", "GCC_ARM", "IAR"],
         "progen": {"target": "xdot-l151cc"},
         "device_has": ["ANALOGIN", "ANALOGOUT", "I2C", "I2CSLAVE", "INTERRUPTIN", "PORTIN", "PORTINOUT", "PORTOUT", "PWMOUT", "RTC", "SERIAL", "SLEEP", "SPI", "SPISLAVE", "STDIO_MESSAGES"],
-        "default_lib": "std",
+        "default_build": "std",
         "release_versions": ["5"]
     },
     "MOTE_L152RC": {