By Lawrence Delevingne and Marc JonesJuly 23 (Reuters) - Oil prices spiked to $100 a barrel on Thursday for the first time since May, while major tech giants knocked U.S. stocks lower and Europe's borrowing costs surged to long-term highs in an unsettling day across markets. Tesla shares tumbled around 14% on Thursday after it posted its first cash burn in two years. Alphabet fell about 7%, with the Google parent also burning through cash while ‌saying it would ramp up AI spending for the year by ⁠another $15 billion, to $200 billion. Investors have rewarded the so-called hyperscalers with lofty valuations on expectations of big revenue gains, but some are now outspending their operating cash flow. EUROPEAN BORROWING COSTS RISEEurope's government borrowing costs rose to long-term ​highs as reignited inflation worries prompted some hawkish signals from the European Central ‌Bank, although the bank held rates steady at 2.25%.